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438 Cards in this Set
- Front
- Back
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What did Robert Boyle propose? |
Some substances couldn't be made any simpler (chemical elements) |
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What did John Dalton say? |
Elements are composed of indivisible atoms and all atoms within an element are identical |
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What did Henry Bacquerel discover? |
Radioactivity , atoms are therefore divisible as particles come from inside the atom. Electrons were discovered |
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What did Ernest Rutherford prove? |
Atoms are mostly made up of space and they have a central nucleus (gold foil experiment) the mass of an atom is positive due to the protons |
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What is the relative mass of an electron? |
1/1800 |
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What are protons and neutrons known as? |
Nucleons |
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What force holds protons and neutrons together? |
Strong nuclear force |
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What force exists between protons and electrons? |
Electrostatic force (weaker than nuclear force) |
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What symbol represents mass number? |
A |
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What symbol represents atomic number? |
Z |
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What does the atomic number represent? |
The number of protons |
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What is the number of protons equal to? |
The number of electrons |
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What is the mass number? |
Sum of the protons and neutrons |
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What are isotopes? |
Different atomic forms of the same element which have the same number of protons but a different number of neutrons |
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What are the names of the orbitals? |
s p d f |
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How many electrons can each orbital hold? |
2 |
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How do the orbitals fill up? |
Starts with 1s and carries on in ascending order |
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What is the exception to this? |
4s is filled before 3d because it has slightly less energy |
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What atoms are the exception to the 4s 3d rule? |
Copper and chromium |
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How do the electrons move in an orbital? |
One spins clockwise and the other anticlockwise |
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How many electrons can be held by the p orbitals all together? |
6 |
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How many electrons can be held by the d orbitals all together? |
10 |
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Electrons dont like.. |
To be in pairs so they fill up seperate orbitals before paring up ( up arrows first) |
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Which orbitals are electrons lost from when forming ions? |
Highest energy level |
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What is the exception to that? |
Electrons are lost from 4s before 3d |
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What is coppers 3d and 4s arrangment? |
4s1 3d10 |
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What is chromiums 4s and 3d arrangment? |
4s1 3d5 |
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How is the full structure shortened? |
Using noble gases |
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What is the first ionisation energy? |
The energy required to remove a mole of electrons from a mole of atoms in a gaseous state and is measured in KJmol-1 |
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What is the second ionisation energy? |
Energy required to remove the second electron |
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What does it take less energy to remove the first electron? |
Further away from the attraction of the nucleus and there is more shielding |
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What happens to the atoms size as you go down group 1? |
Increase |
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Why does the ionisation energy decrease as you go down group 1? |
Further away from nucleus and more shielding as the atoms get bigger |
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Are they more reactive as you go down the group? |
Yes |
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What ions do group one form? |
Positive |
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What is the word for positive ion? |
Cation |
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What is the word for negativs ion? |
Anion |
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What do ionisation energies provide evidence for? |
The existence of sub shells |
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What is the ionisation energy trend in group 2? |
Decreases as you go down the group |
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Why? |
Atomic radius increases so shielding increases and distance from the nucleus increases |
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What is the ionisation energy trend in period 3? |
Fluctuates but however it generally increases |
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Why? |
The atoms gain more protons are you go across the period, therefore they gain a larger nuclear charge so the electrons are pulled in which gives the atom a smaller atomic radius. But when a new orbital is filled the radius increases again. Ionisation energy also decreases when theres a pair of electrons (repulsion) |
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What doesnt the electron pair rule apply to? |
Full orbitals |
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How are ionisation energy equations written? |
Like half equations with the gas symbol |
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Why do isotopes react the same way? |
They have the same electron configuration |
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How do you calculate relative atomic mass from isotope mass and abundance |
Multiply mass by abundance and add together. Then divide by total abundance |
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What does the mass spec give information about? |
Relative isotopic mass and abundance of isotopes |
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What can this data be used for? |
Identify elements and determine relative molecular mass |
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What is Ar? |
The mass of an atom |
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What is Mr? |
The mass of a molecule |
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What is step 1 of mass spec? |
Ionisation. |
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What is bombardment? |
The sample is vapourised and high energy electrons are fired from an electron gun at the sample. Electrons are knocked off so the atoms become positive ions |
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What is electro spray? |
The sample is dissolved into a volatile solvent and a high voltage is applied. The solution is pushed through a fine hollow needle. Positive Droplets form which evaporate get smaller and smaller until they form positive ions. |
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Why is a vacuum necessary in ionisation? |
Prevents ions from coliding with molecules in the air and prevents air molecules ionising and registering at the detector |
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What is step 2 of mass spec? |
Acceleration |
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How does acceleration occur? |
The positive ions are attracted to a negative plate , therefore they accelerate towards it |
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Which ions reach the plate first? |
Lighter and higher charged |
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What is important about acceleration? |
Ions must have a constant kinetic energy |
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What is step 3 of mass spec? |
The ions pass throhgh a hole in the negatively charged plate. They form a beam in a tube and travel towards the detector. (Ion drift) |
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What is step 4 of mass spec? |
The time of flight ( TOF) is recorded by the detector and the positive ions gain electrons and this causes a current to flow. The current is sent to the computer |
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What is the last step of mass spec? |
The computer uses this information to form a mass spec graph |
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What is the equation to find Ar? |
Average mass of 1 atom / 1/12 mass of 1 atom of carbon 12 |
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Why is ionisation energy endothermic? |
Energy is required ( taken in) to overcome attractive forces between the negative electron and the positive nucleus to remove the electron from the atom |
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How can you identify an element from its ionisation energies? |
Look for the biggest jump , this is what group it's in as the big jump is the change from energy levels |
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The larger the atomic radius the weaker the... |
Attraction of the electron to the ion |
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What isoptopes are deflected the most by a magnetic field? |
Ones with the lowest mass |
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What are the different blocks of the periodic table? |
Left is s , transition metals are d and right is p |
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What is an ionic bond? |
Electrostatic attraction between two oppositely charged ions in a lattice |
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What happens to electrons during an ionic bond? |
They are donated and accepted to form ions |
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What ions do metals form? |
Positive |
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What ions do non-metals form? |
Negative |
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How can you tell what ion an element will form? |
By looking at it's group |
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What are the 5 common ions? |
Sulphate , hydroxide , nitrate , carbonate and ammonium |
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Which ions have negative charge? |
Hydroxide ( OH) nitrate ( NO3) |
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What ions have a double negative charge? |
Sulphate ( SO4) carbonate ( CO3) |
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What ion has a positive charge? |
Ammonium ( NH4) |
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How do you construct the formula of an ionic compound? |
State which ions will be formed by the elements Equal their charges like a simultaneous equation |
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What are the properties of an ionic compound?(4) |
High melting&boiling point Good conductor of heat and electricity due to free ions in molten/aqueous state Soluble Brittle due to same charges repelling when struck |
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What is the equation to find Mr? |
Average mass of one molecule / 1/12th mass of an atom of carbon 12 |
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Why is the term relative 'formula' mass used for ionic compounds? |
Only covalent bonded compounds for molecules. Ionic compounds are not molecules |
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What is the definition for relative atomic mass? |
The weighted average mass of an atom of an element , taking into account it's naturally occuring isotopes, compared to 1/12 of the atomic mass of an atom of carbon 12 |
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How do you work out the mass of a compound? |
Add together the mass of each atom in the compound (period table) |
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How do you work out the percentage mass of an atom in a compound? |
Divide the mass of the atom by the total mass of the compound. Then multiply by 100 |
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What is the equation for moles? |
Mass / relative atomic/molecular mass |
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What is Ar and Mr unit? |
gmol^-1 |
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What is the value of one twelfth of carbon 12? |
1 |
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What is the value of Avogadro's constant? |
6.022 x 10^23 |
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What is Avogadros constant? |
The number of atoms in 12g of carbon 12 |
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What is another word for Avogadros constant? |
One mole |
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What must each side of a chemical equation balance? |
Atoms cannot be created or destroyed |
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What is molar mass? |
The term used to describe relative atomic/formula mass |
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What is the equation to work out the number of particles? |
Number of particles = (mass(g) / molar mass(Ar/Mr) ) x avogadros constant |
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What resolution should molar masses be given to? |
1 d.p |
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What resolution should number of particles be given to? |
Highest degree of accuracy that is shown in the question |
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When is 0 a significant figure? |
When it comes after a number |
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What is a covalent bond? |
Where atoms share electrons (outter shells) to form a noble gas arrangment |
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What types of atoms are involved in covalent bonding? |
Non-metals |
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How many electrons does a single covalent bond involve? |
2 |
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How many electrons does a double covalent bond involve? |
4 |
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How many electrons does a triple covalent bond involve? |
6 |
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What do covalent compounds form? |
Molecules |
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What is the other type of covalent bond known as? |
A dative/co-ordinate bond |
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What is the difference between a covalent bond and a dative covalent bond? |
Covalent bond involves electrons from both atoms outter shells but dative covalent has electrons from only one atom (lone pairs) |
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How can covalent bonds be represented on a diagram? |
Black lines / dot-cross diagram |
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What are 4 properties of simple covalent substances? |
Low melting&boiling point due to weak intermolecular forces Cannot conduct electricity Liquid/gas at room temp Insoluble |
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How is a dot cross diagram shown for a dative bond? |
The pair electrons in the bond is both dots or both crosses as they come from one atom (lone pair) |
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How else can a dative bond be shown in a diagram? |
As an arrow instead of a line , the arrow shows the direction of where electrons have come from |
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What joins to NH3 to form NH4 + |
A H+ ion |
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What does the group number of a metal indicate? |
The charge it will form |
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Why can metals carry a charge? |
They have delocalised electrons which can move throughout it's structure |
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What happens when a voltage is applied to a metal? |
Electrons move towards positive terminal , as theyre negatively charged, a current flows |
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Why are metals strong? |
Strong metallic bonds |
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What is a metallic bond? |
Attraction between positive metal ions and delocalised electrons in a lattice |
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How is the strength of metallic bond increased? |
Nuclear charge increases ( pulls electrons in and more energy required to overcome attraction between positive nucleus and electrons) Metallic radius is smaller ( electrons closer to the nucleus so the attractive forces are stronger) |
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Are metals malleable and ductile? |
Yes |
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Why? |
When distortion occurs the ions remain in the same environment as the charges do not repel. They can move over eachother and change shape (LAYERZ CAN SLIDE) |
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Ions which have a greater charge and a smaller radius have more... |
Electrons in their delocalised system |
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How do you draw the structure of a metal? |
Circles with + in to represent ions and smaller circles throughout to represent electrons |
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What are the four types of crystal? |
Ionic , metallic , giant covalent (macromolecular) , simple covalent (molecular) |
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What cant covalent structures conduct electricity? |
They dont have any delocalised electrons which can carry a charge |
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Why do metals have a high melting point? |
Strong metallic bond. Strong attractive forces between delocalised electrons and positive ions |
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Does benzene have delocalised electrons? |
Yes |
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What is concentration measured in? |
Mol dm^-3 |
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What is a different equation to work out moles? |
Moles = concentration x volume |
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What is volume measured in? |
Dm^3 |
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How do you convert cm^3 to dm^3 |
÷1000 |
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Are dm bigger than cm? |
Yes |
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If you have an equation and moles of one substance, how do you work out moles of the other substance? |
Look at the ratio |
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How much volume does 1 mole of gas at standard condition take up? |
24 dm^3 (100k Pa 298 K) |
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What is the ideal gas equation? |
pV = nRT |
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What is the gas constant? |
8.31 JK^-1mol^-1 |
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What is pressure measured in (p) ? |
Pa (pascals) |
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What is volume measured in?(V) |
M^3 |
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What does n stand for? |
Moles |
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What does R stand for? |
Gas constant |
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What is temperature measured in(T)? |
Kelvin |
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What happens to a gas when you increase temperature and pressure? |
Volume increases |
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How do you covert KPa to Pa |
X1000 |
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How do you convert cm^3 to dm^3 |
÷1000 |
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How do you convert dm^3 to m^3 ? |
÷1000 |
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Therefore , how do you convert cm^3 to m^3 ? |
÷ 1 000 000 |
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How do you convert celius to kelvin? |
Add 273 |
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What is empirical formula? |
The simplest whole number ratio of atoms of each element present in a compound |
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What is molecular formula? |
The actual number of atoms of each element in one molecule of a compound |
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How do you work out empirical formula? |
Work out moles. Put them in a ratio , divide by smallest to get ratio in whole numbers |
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How do you work out molecular formula? |
Molecular mass / mass of empirical formula. Multiply empirical formula by this number |
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Should you leave your answers in standard form? |
Yes |
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What is electronegativity ? |
The power of an atom to attract the pair of electrons in a covalent bond towards it |
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What scale is electronegativity measured on? |
The pauling scale |
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What number is low EN and what is high? |
1 is low and 4 is high |
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What EN value do noble gases have and why? |
0 because theyre unreactive |
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What is electron density? |
The way negative charge is distributed in a molecule. The probability you will find electrons in a certain place |
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What 3 factors affect electronegativity and why? |
Nuclear charge - as nuclear charge increases so does EN as the protons attract the electrons Distance between nucleus and outter electron - smaller distance means stronger EN Shielding - as shielding increases EN decreases |
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Where is EN highest on the periodic table? |
Up and across |
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What does delta positive mean? |
Slightly positive |
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What does delta minus mean? |
Slightly negative |
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Why will covalent bonds with same atoms be non-polar? |
Same EN so electrons will be shared equally and the molecule will be symmetrical |
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Why will covalent bonds with different atoms be polar? |
Large difference in EN so electron distribution is unequal making it unsymmetrical |
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What is an unsymmetrical molecule known as? |
A permanent dipole |
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Why wont all molecules with polar bonds have a permanent dipole? |
Charges cancel as sometimes symmetrical ( electrons pulled either side so they are spread out evenly) |
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The what of the molecule determines whether it is polar or not? |
Shape |
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What are the three intermolecular forces? |
Van der waals , dipole-dipole , hydrogen bonding |
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What is the strongest IMF? |
Hydrogen bonds |
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What is the weakest IMF? |
VDW |
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How does dipole dipole work? |
Attarction between opposite slightly charged parts of polar molecules |
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What IMF occurs between all molecules? |
VDWs |
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How does VDWs work? |
Electrons are constantly moving , therefore non-polar molecules become polar for an instant. One molecule becoming polar causes neighbouring molecules to also become polar and a temporary dipole-dipole force is formed |
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How does hydrogen bonding work? |
Attraction between delta positive hydrogen and delta minus lone pair of a FONS |
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Substances with hydrogen bonds have higher... |
Melting and boiling points |
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Why? |
More energy required to overcome strong attractive forces |
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The bigger the molecules , the bigger the... |
VdWs , as theres more electrons so a greater attraction is formed |
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How do you draw hydrogen bonds? |
Vertical dashed lines |
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Why is ice less dense than water? |
When the molecules of water slow down they arrange themselves in a crystal structure and the water molecules spread out to form an open lattice |
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What is a practical reason for the yield being lower than expected? |
Product lost when weighing or blown away by gas produced |
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Do you include coefficients in Mr? |
NO BECAUSE IT EFFECTS STOICHIOMETRY |
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Why should equations alwayz be balanced? |
Atoms cannot be created or destroyed |
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What do balanced equations tell us about moles? |
The ratio things react in ( moles) |
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What are the state symbols? |
(S) solid (l) liquid (g) gas (aq) dissolved in water/aqeous |
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Are the masses the same on each side of the equation? |
Yes |
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What do you do for ionic equations? |
Write out the seperate ions |
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What do you do after you have written out the seperate ions? |
Cancel the ones that appear on both sides |
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What are ions that are cancelled out called? |
Spectator ions |
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What needs to be the same on both sides of an ionic equation? |
The charges |
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How do you carry out a reacting masses calculationz? |
-balance the equation -look at the ratio -calculate moles of known substance using mass/Mr -use ratio to calculate moles of unknown - use moles = mass/Mr to find unknown mass |
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How do you carry out titration calculations? |
-balance -work out moles with info -use ratio to work out moles of unknown -use m= cxv to calculate unknown |
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What is the atom economy calculation? |
Mass of desired product /total mass of reactants x 100 |
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What percentage of atom economy is better for the environment and why? |
A high percentage as it means less waste |
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If theres only one product what is the atom economy? |
100% |
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What is the yield equation? |
Actual yield / theoretical yield x100 |
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What does a higher yield mean? |
A more efficient reaction |
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What four things can affect yield? |
Unwanted reactions , mixture lost , reversible reactions , incomplete reactions |
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What is the danger of a reaction that releases gas occuring in a sealed flask? |
Pressure increases so the flask may explode or break |
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What does NO2 contribute to? |
Acid rain |
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Why is an excess used in reactions? |
To make sure there is a complete reaction |
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What is another word for melting? |
Fusion |
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What is another word for boiling? |
Vaporisation |
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What are the arrangement of particles in the three states? |
Regular in solid and random in liquid and gas |
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What is evidence for this? |
Crystals have straight edges and liquids and gases fill containers of any shape |
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What is the spacing of these particles in the three states? |
Close in solid and liquid. Far apart in gas |
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What is the evidence for this? |
Solids and liquids are hard to compress whereas gases are easily compressed |
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What is the movement of the particles in the three states when energy is supplied? |
Solids vibrate around a fixed point , liquids jostle and gases move rapidly |
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What is the evidence? |
Solids expand on heating , liquids evaporate , gases exert pressure |
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What is the bonding in ionic crystals and whats an example? |
Electrostatic attraction between oppositely charged ions in a lattice. NaCl is an example. |
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What are the properties of ionic crystals? |
-Soluble -Can conduct electricity and heat when molten -High melting and boiling point due to many strong ionic bonds -Brittle due to repelling |
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What is the bonding in metallic crystals and what is an example ? |
Strong metallic bonds between positive ions and a sea of delocalised electrons , magnesium is an example of a metallic lattice |
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What are the properties of metallic crystals? |
Can conduct electricty and heat Malleable and ductile due to sliding layers High melting and boiling point due to strong metallic bonds |
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What is bonding in molecular crystals and an example? |
Covalent bonds between atoms but weak van der waals between molecules. Iodine is an example (I2) |
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What are the properties of molecular crystals? |
Low melting and boiling points due to weak VDWs Do not conduct electricity Soft and easy to break |
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What is the bonding in macromolecular crystals and what is an example? |
Many strong covalent bonds. Diamond is an example |
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What are diamond and graphite made of? |
Carbon |
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What are the structure and properties of diamond? |
Each carbon atom is bonded to 4 other carbon atoms It has a very high melting and boiling point It is very hard Doesnt conduct Unreactive Insoluble |
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What is the structure and properties of graphite? |
Each carbon atom is bonded to another 3 carbon atoms. Delocalised electrons that can conduct electricity and heat VDWs between layers of graphite so is soft and flaky High melting and boiling point Insoluble |
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What changes the shape of a molecule/ion? |
The number of electrons |
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What is the electron pair repulsion theory? |
Bonding pairs and lone pairs repel eachother and place themselves as far apart from each other as possible to minimise repulsion |
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What does the electron pair repulsion effect? |
The size of bond angles |
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What bond pairs have the greatest repulsion? |
Two lone pairs |
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What bond pairs have the lowest repulsion? |
Two bond pairs |
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How do you work out the shape of a molecule? |
Draw a dot-cross diagram Count the number of electron pairs around the central atom |
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What is the bond angle of a molecule with 2 electron pairs and what is the shape called? |
180 degrees , linear |
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Bond angle and name of molecule with 3 electron pairs? |
120 degrees , trigonal planar |
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Bond angle of 4 electron pairs? |
109.5 degrees |
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For four bonding pairs what is the shape? |
Tetrahedral |
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For 3 bonding pairs and one lone pair? |
Pyramidal |
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For two bonding pairs and two lone pairs? |
Bent |
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How many degrees do you subtract off of the bond angle for each lone pair? |
2.5 |
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What is the shape and bond angle of molecule with 5 electron pairs? |
Trigonal bipyramid. 90 degrees between above and side atoms , 120 degrees between side atoms |
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Shape and bond angle of molecule with 6 electron pairs? |
Octahedral , 90 degrees |
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What does a triangle bond represent? |
Coming towards you |
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What does a dashed line bond present? |
Behind |
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What does a droplet represent? |
Lone pair |
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What molecule is an exception? |
Ethene , it is trigonal planar |
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What about 4 bonding pairs and two lone pairs , how will it look? |
Lone pair on bottom and top |
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What is the shape of this? |
Square planar |
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Energy is taken in to... |
Break bonds |
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Energy is given out when... |
New bonds are formed |
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What are exothermic reactions? |
Reactions that give out more energy than they take in (form more bonds) |
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What are endothermic reactions? |
Reactions that take in more energy than they give out (break more bonds) |
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What is the most common form of energy? |
Heat |
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What is an example of an exothermic reaction? |
Neutralisation |
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What is an example of an endothermic reaction? |
Thermal decomposition |
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What unit is energy measured in? |
Kjmol^-1 |
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When fuels are burnt ,what type of reaction is this? |
Largely exothermic |
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Why are state symbols important when talking about energy released? |
Energy released can vary depending on state , e.g. gas and liquid |
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What is enthalpy change? |
A measure of heat energy given out or taken in when a chemical or physical change occurs at a constant pressure |
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What does delta triangle mean? |
Change |
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What three factors effect heat energy given out by a reaction? |
Room Temperature , pressure and concentration of reactants |
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What are the standard conditions for a reaction? |
100kpa and 298K |
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How is standard condition written? |
Delta H theta 298 |
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How do you work out enthalpy change? |
Energy of products - energy of reactants |
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What enthalpy change will exothermic reactions have? |
Negative |
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Why? |
Products have less energy than reactants |
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What enthalpy change value will endothermic reactions have? |
Positive |
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Why? |
Products have more energy than reactants |
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What does increasing pressure do to the amount of energy released? Why? |
Decreases it as gas released has to push against atmosphere and this requires energy |
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What is the standard enthalpy of combustion? |
The enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions and states |
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What is the standard enthalpy of formation? |
The enthalpy change when one mole of a substance is formed from its constituent elements under standard conditions and states |
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What is thermochemistry? |
The study of heat changes during chemical reactions |
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What can activation energy be represented by? |
Ea |
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What is activation energy? |
The minimum amount of energy required for a particle to react in a collision |
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What is activation energy (graph wise) ? |
Energy difference between enthalpy of reactants and transition state |
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What 5 factors increase rate of reaction? |
Temperature , concentration , pressure , surface area , catalyst present |
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Why does increasing the surface area increase the rate of reaction? |
More of the reactants particles are available at one to time for other particles to collide with |
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What does a catalyst do to a reaction? |
Lowers the activation energy |
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What is a catalyst? |
A substance that alters the rate of a chemical reaction but is not used up in the reaction |
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What does increasing the rate of reaction do to the collisions? |
Increases the number of successful collisions in a certain period of time |
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Why do most collisions not result in a reaction taking place? |
The particles do not have enough energy (they need activation emergy or above) for successful collisions to occur |
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Do all particles have energy? |
Yes |
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Define rate of reaction? |
Change in concentration of reactants/products in a given time |
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Where is the transition state on a graph? |
Top of peak |
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Where does the Ea go from on a graph? |
Reactants to transition state |
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What is another word for the transition state? |
Activated complex |
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What does the Maxwell-Boltzmann distribution show? |
Energies of the particles in a gas/solution |
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What else does it show? |
The number of particles in a gas/solution and how many of them have a certain amount of energy |
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Why does the graph begin at the origin? |
All particles have energy so zero particles have zero energy |
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What is the peak of the graph? |
The most probable energy of the particles |
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What does the area under the curve represent? |
The number of particles in the sample |
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Where is the average energy on the graph? |
To the right of the probable energy |
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What are the areas under the curve to the right and the left of the average energy? |
Equal |
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Where is Ea on the graph? |
The far right of the average energy |
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What is to the right of the Ea (in terms of area)? |
The number of particles that have enough energy to react if they collide ( successful collisions) |
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What happens to the graph as the temperature is increased? |
Peak lowers and moves to right as energy increases Area under curve stays same |
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What happens to probable energy and area after Ea? |
Probable energy increases and area under Ea increases because more particles have enouh energy to react |
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Why does the area under the graph stay the same? |
The number of particles doesnt change |
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What happens to the graph when the temperature is decreased? |
Peak rises and moves to left because energy decreases and area under curve stays the same |
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What happens to probable energy and area under curve after Ea? |
Probable energy decreases and area decreases because less particles have enough energy to react |
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What is the equation for energy change? |
Q = mcAT |
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What is Q and its unit? |
Energy change (J) |
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What is m and the unit? |
Mass(g) |
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What is c and the unit? |
Specific heat capacity ( Jg^-1K^-1) |
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What is AT and the unit? |
Temperature change (K) |
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What does molar mean? |
Per mole |
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What is molar enthalpy change? |
The energy change per mole of a substance |
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What is molar enthalpy change measured in? |
Kjmol^-1 |
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What happens to particles when kinetic energy is increased? |
Their movement increases |
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What is the difference between temperature and heat? |
Temperature is the average kinetic energy of particles in a system. Heat is the total energy that the particles have |
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Therefore a substance with more particles... |
Has more heat even if it has a lower temperature |
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What is specific heat capacity? |
The amount of energy needed to raise the temperature of 1g of a substance by 1K |
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What are two examples of school calorimetry? |
A polystyrene cup with a thermometer in. Heating weat using a spirit burner |
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How would you improve a school calorimetry? |
Prevent heat loss to make your results more reliable. Use insulation and a draught screen |
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Why is polystyrene a good insulator? |
It has a low heat capacity so it cannot absorb large amounts of heat , this keeps the heat where you want it |
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What are 3 examples of exothermic reactions? |
Combustion , neutralisation , displacement |
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How would you go about working out molar enthalpy change? |
Work out energy change and then moles. Divide energy by moles. |
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What units must your energy be in , in these calculations? |
KJ |
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How do you convert J to KJ? |
Divide by 1000 |
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What happens in a displacement reaction? |
A more reactive metal replaces a less reactive metal in a compound |
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What is a cooling curve? |
A graph that allows heat loss as heat will still be lost even if you use insulation |
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How do you plot a cooling curve? |
Firstly begin by leaving your substances to stand and record temp to see if its constant (draw line of best fit for this) Mix for reaction and temp will rise as its exothermic Then record temp for a while after to see decrease (draw line of best fit) |
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How do exothermic reactions effect the surroundings? |
Warm them as they release heat |
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How do endothermic reactions effect the surroundings? |
Take in heat so they cool the surroundings |
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What is the specific heat capacity of an aqeous solution? |
The same as water ( 4.2/4.18) |
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1g = |
1cm^3 |
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Why may calculated enthalpy change be incorrect? |
It doesnt take heat loss into account |
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What is the specific heat capacity of water? |
4.2 or 4.18 to be more accurate |
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What do you need to remember to do when you have your enthalpy change value? |
State whether it is exo or endo by putting a - or + |
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What does dissolution mean? |
Dissolving a substance into water |
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Why could a small increase in temperature massively increase the rate of reaction? |
Particles reach activation energy so a lot have enough energy to react |
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How does the maxwell boltzmann graph change with a catalyst? |
Ea moves to left as activation energy is lowered (larger area under curve so more particles with enough energy to react via successful collisions) |
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Define enthalpy change? |
Heat energy change under a constant pressue |
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What factor other than heat loss makes something less exothermic? |
Incomplete combustion |
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When do we need to use Hess's law to find out enthalpy change? |
When enthalpy change cannot be measured directly |
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What does Hess's law state? |
The enthalpy change for a chemical reaction is the same regardless of the route taken to get from the reactants to the products |
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Therefore route 1 = |
Route 2 |
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So how do we measure enthalpy change if we cant measure it directly? |
Measure the enthalpy change of a different route |
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What is it called when we use Hess's law? |
A thermochemical cycle |
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What is step one of a thermochemical cycle? |
Balance route 1 and add state symbols |
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Step? |
Show route 2 and include energy changes and labelled arrows |
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Step 3? |
Route 1 = route 2 Add energy changes together Check arrow directions |
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What two types of enthalpy changes can we work out using a thermochemical cycle? |
Enthalpy change of formation and enthalpy change of combustion |
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What do we put as route 2 for formation? |
The balanced constiuent elements (diatomic form) |
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Which way do the arrows go up in formation? |
Up as the elements form the compounds |
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What compounds are not included in formation? |
Ones made of one type of element |
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What do we put as route two for combustion? |
CO2 + H2O |
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Which way do the arrows go in combustion? |
Down as compounds form this when burnt with oxygen |
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Which compound/element doesnt combust? |
Oxygen |
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In which enthalpy change thermochemical cycle can there be more than two arrows? |
Combustion |
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How can you work out formation from combustion? |
Work out the change of the whole cycle |
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What is enthalpy change of formation equal to? |
Combustion enthalpy change |
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Why may values be incorrect? |
Rounding errors in data |
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Do the coefficients matter in enthalpychange? |
Yes |
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In chemical equilibria what type of reactions are there? |
Reversible reactions |
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What does it mean when a reaction is reversible? |
The formed products can react again to reform the reactants and this continues |
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What happens when equilibrium has been reached for a reversible reaction? |
The rate of the forward and reverse reaction are equal. The amount of reactants and products are equal |
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What type of system is this? |
A closed system |
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How do exothermic and endothermic reactions apply to reversible reactions? |
If one way is exo then the other way will be endo vice versa (enthalpy change values may be given but if not we assume forward is exo) |
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What is le chateliers principle? |
If a system is disturbed the equilibrium will move in the direction that tends to reduce the disturbance |
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Do catalysts have an effect on equilibrium? |
No , they only decrease the time for equilibrium to be reached |
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What happens to equilibrium when temperature is increased? |
It moves to side where the endothermic reaction is as endo takes in heat so this would reduce the disturbance |
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What happens to equilibrium when pressure is increased? |
Equilibrium will move to the side with less molecules |
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What happens if molecules are equal either side? |
Will not effect equilibrium |
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What happens if concentration is increased? |
Equilibrium will move to where there is less conc to balance the concs |
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What is important about the states in equilibria? |
Must all be the same , all gas for pressure and all aq for concentration |
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What can physically be observed in an equilibrium reaction? |
Colour change |
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What are the most common conditions for industrial processes? |
20,000 kPa and 673 K |
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What can explain how we obtain the best yield? |
Le chateliers principle |
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However.. |
Compromises need to be made due to costs and rate of reaction |
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What form are catalysts used in industrial processes? |
Larger surface area to increase ROR |
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What is a dynamic equilibrium? |
Rates are same and are happening simultaneously |
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Define mean bond enthalpy |
Heat energy required to form and break covalent bonds , it is an average of many different molecules values |
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Do bond enthalpies vary between molecules? |
Yes |
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Therefore... |
An average is calculated |
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What is bond dissociation enthalpy? |
Bond enthalpy in a gaseous state |
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Energy to break bond = |
Energy to make bond |
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How do you carry out a bond enthalpy calculation? |
Draw out the structures Calculate total bond energy either side Reactants -products Check signs are correct |
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Why do average bond enthalpies vary? |
Different data is used to calculate average |
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Therefore the bond enthalpy method gives a... |
Approximation |
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Whats more reliable hess cycles or bond enthalpies? |
Hess cycles |
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For Kc to be true reaction must be... |
Reversible , in all the same states and approach equilibrium |
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How do you put a reaction into the formula to find Kc? |
Products on top and reactants on the bottom with each concentration to the power of the number of moles/coefficient |
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What is Kc not effected by? |
Catalyst and change in concentration |
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How do you work out units for Kc? |
Indices laws , unit will be similar to concentration unit |
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How do you calculate Kc? |
Write out balanced equation Work out moles at equilibrium Work out concentration Put into formula made from equation Work out units |
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What do we assume the products initial moles to be? |
0 |
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How do you work out equilibrium moles from initial moles? |
Change and opposite signs for reactants and products , multiply change by coefficients |
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Does changing temperature effect Kc? |
Yes |
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How? |
Equilibrium will shift to left or right depending on exo/endo and if temp was increase/decrease. This will decrease /increase products . Products/reactants = Kc so if moves to right Kc increases and moves to left Kc decreasew |
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How can you estimate whether reactants or products are larger? |
Look at Kc value and products/reactants |
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Formula of ethanol? |
C2H5OH |
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Formula of ethanoic acid? |
CH3CO2H |
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Formula of ethyl ethanoate? |
CH3CO2C2H5 |
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When do you use bombardment and electro spray? |
Bombardment for small molecules and electro spray for large molecules |
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What happens to the current in mass spec if the abundance is larger? |
It increases |
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What are the axes of a mass spec graph? |
M/z ratio on x axis and abundance on y axis |
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How is m/z ratio effected by ions with a greater charge? |
M / z so for 2+ youd do mass divided by two |
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In Ar calculations how do you find abundances? |
Use variables y and (y-1) to sub into equation |
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What type of molecules show Mr instead of Ar on mass spec? |
Diatomic molecules |
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What is fragmentation? |
Molecule is split up into bits due to bombardment in mass spec so different mass peaks. |
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What is the general rule for the amount of electrons in one shell? |
2n^2 where n=shell number |
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How do you convert moldm^-3 to gdm^-3? |
Multiply by the Mr |
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What happens to coefficients in atom economy? |
You take them into account |
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What do you do when working out x values of H2O? |
Ratio of moles sometimes |
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What shape is ice? |
Tetrahedral |
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What does gas dissipate? |
Random movement |
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Maxwell boltzmann distribution the energies of.. |
Gassed and liquids |
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What is the equation of rate? |
1/time |
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Alternatively you can... |
Work out gradient of tangent to the graph |
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What solid does ethene form at a high pressure with a large Mr? |
Polyethene |
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What state symbols should you use in equations? |
Common sense unless specified otherwise |
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How do you calculate percentage uncertainty? |
Uncertainity/ total volume x100 |
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Where is dynamic equilibrium on a graph? |
Where both lines are horizontal |
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What effect do bubbles in the burette have on titre value? |
Increase it |
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What else accelerates the ions in mass spec? |
An electric field |
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What is redox short for? |
Reduction-oxidation |
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Therefore a redox reaction involves? |
Reduction and oxidation |
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If reduction takes place... |
Oxidation must also take place (vice versa) |
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What happens to electrons in oxidation? |
They are lost |
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What happens to electrons in reduction? |
They are gained |
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What do oxidising agents do? |
Accept electrons |
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What do reducing agents do? |
Donate electrons |
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What do oxidation states show in ionic compounds? |
The transfer of electrons |
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In molecules? |
The electronegativity |
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OS of element? |
0 |
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OS of H? |
+1 |
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Exception for H? |
-1 in metal hydrides |
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OS for Group 1? |
+1 |
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Os for group 2 |
+2 |
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Os for aluminium? |
+3 |
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Os state for O? |
-2 |
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Exception for O? |
-1 in hydrogen peroxide and +2 in OF2 |
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Os for F? |
-1 |
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Os for Cl? |
-1 |
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Exception for Cl? |
Positive with oxygen and fluorine |
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What is the sum of the oxidation states for a compound? |
0 |
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Unless? |
The compound has a charge |
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What is the phrase we use to work out complex half equations? |
OxiBEWHyM |
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How do you add half equations together to make a redox equation? |
Multiply to balance same electrons and then add and cancel what you can |
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Classic examples of oxidising and reducing agents? |
Oxygen and hydrogen |
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What do we do if we don't know the volume in Kc calculations? |
The volumes cancel out via algebra |
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How can you measure volume of water without a balance? |
Water had a known density |
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Why is using droplets inaccurate? |
They vary in size |
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Does time taken increase with a lager flask (titration) ? |
Yes |
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In equilibrium the concs are constant but they are not... |
Equal |
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Reason for heat loss apart from loss to atmosphere and incomplete combustion? |
Transfer to copper calorimeter , evaporation of water |
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Why may uncertainity be adequate? |
The temp change is greater than the uncertainty |
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Is SO2 soluble in water? |
Yes |
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Is SO2 a basic oxide? |
No |
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What should be used to avoid toxic fumes? |
Fume cupboard |
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Why cant formation of carbon monoxide be directly measured? |
Carbon dioxide may form |
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With hydrous do you include coefficients in Mr? |
Yes |
