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90 Cards in this Set
- Front
- Back
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What are all nuclear reactions? |
Exothermic |
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What are nuclear reactions involving large quantities of energy? |
Fission + Fusion |
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When does Fusion occur? |
Nuclei of small atomic mass combine to form larger, heavier nuclei |
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What is the product of a fusion reaction? |
Heavier, more stable nucleus |
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What are fusion reactions responsible for? |
Release of energy in stars + sun |
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Which fusion reaction occurs in sun? |
Hydrogen forms helium + energy under extremely high pressure |
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A X what is A? Z |
Mass # ( # of protons + # of neutrons) |
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A X what is Z? Z |
Atomic number ( # of protons) |
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What happens during fission |
The process of using a neutron to split a nucleus of high atomic mass into 2 nuclei with smaller masses |
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Which elements can undergo fission? Why? |
Elements above atomic #88 + because they are unstable |
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Does fission normally occur in nature? |
No |
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What else does fission produce? |
Million times more energy than in chemical reaction |
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What happens in power plants? |
Fission of uranium - 235 (produces electricity |
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What happens in a chemical reaction? |
Chemical bonds are broken + new bonds are formed to produce the products |
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Does bond breaking or bond formation release energy? |
Bond formation releases energy |
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Why does bond breaking require energy? |
The potential energy of bonds is lower than the potential energy of lone atoms. |
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Why must the amount of energy in a chemical system + surroundings be the same before + after a chemical reaction? |
Law of conservation of energy |
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What is exothermic? |
A chemical reaction that releases energy to its surrounding |
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Describe the products of an exothermic reaction |
lower PE, stronger bonds |
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What happens to the temp of surroundings when an exothermic reaction releases thermal energy? |
Temp increases |
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What is an endothermic reaction |
Chemical system absorbs energy from surroundings and increases its potential energy |
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Describe products products of endothermic reactions |
Higher PE, weaker bonds |
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Can energy be converted from one form to another? |
Yes |
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What is the law of conservation of energy? |
Energy cannot be created/destroyed |
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Which 2 parts is the universe divided into? |
Chemical system + surroundings |
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What is an open system> |
Energy + matter are free to enter and leave the system |
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What is a closed system? |
Energy can enter and leave but matter cannot |
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What is an isolated system? |
Matter/energy cannot leave. Impossible to set up a true isolated system on earth. |
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What is thermal energy? |
Total quantity of kinetic + potential energy in a substance |
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What does the quantity of thermal energy of a substance depend on? |
How fast its entities ( atoms, ions, molecules, polyatomic ions) move |
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What happens when a substance warms up? |
Entities move faster, substance absorbs thermal energy |
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What is heat? |
The transfer of thermal energy from a warm object to a cool object |
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What is temperature? |
Measure of average kinetic energy of entities in a substance |
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Why is thermal of an iceberg greater than a cup of hot H2O? |
Billions more water particles |
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What is thermo chemistry? |
The study of energy changes during physical/ chemical changes |
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What is the energy? |
The ability to do work |
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What is work? |
The energy transferred by a force over a distance |
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What is potential energy? |
Energy of a body/system due to its position or composition |
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What is kinetic energy? |
Energy of an object sue to its motion |
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Why is it important to have a clear way to describe if a reaction is endo/exothermic? |
Sometimes enthalpy change is more subtle |
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What is a chemical equation that describes the enthalpy change of a reaction called? |
Thermochemical equation |
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What are the 2 ways enthaply change can be written in a thermochemical equation? |
On products side Written after equation as /_\H= -
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In a potential energy diagram (exothermic) which way does the arrow point (Reactions have higher PE than Products)? |
Down |
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What is enthaply (H)? |
The total amount of thermal energy in a substance |
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Do chemists have a way to measure the enthaply of a given substance? |
No |
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What is enthaply change (/_\H)? |
The energy released/absorbed from surroundings during a chemical/physical change |
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Difference between q and /_\H? |
q=Energy released/absorbed from system /_\H=energy released/absorbed from surroundings |
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How can /_\H be measured using calorimetry data? |
If pressure remains constant, /_\Hsystem =|q system| |
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Ina chemical reaction, how can /_\H be calculated? |
/_\= H products - H reactions |
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Symbol for molar enthalpy change? |
(/_\Hr) |
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What is molar enthalpy change? |
Enthalpy change with physical/chemical/nuclear change with 1 mol of substance |
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What must be the coefficient of a product of formation? |
1 |
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What does the quantity of energy involves in a change depend on? |
quantity of matter that undergoes the change |
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What do you need to obtain to calculate enthalpy change of a substance other than 1 mol? |
Molar enthalpy value (/_\Hr) + then we use formula /_\H = n/_\Hr |
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What is the system composed of? |
Components of the physical or chemical change that occurs |
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What is the one way the scientists can study thermal energy transfers> |
Calorimetry |
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What is calorimetry? |
Procecedd of measuring energy changes during physical or chemical change (experimental) |
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What is a calorimeter? |
Device used to measure thermal energy changes |
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What does a calorimeter consist of? |
-Well insulated reaction chamber (min energy loss) -liquid (usually water) -Constant pressure (since small amount of gas will escape) |
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What do scientists use to studt physical/chemical changes in gas? |
Bomb calorimeter (prevents almost all the gas from esacping? |
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What is a bomb calorimeter particularly useful for studying? |
Combustion |
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Why is sand hotter than water after being in the sun for the same amount of time? |
It has higher specific heat capacity |
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What is specific heat capacity? |
Quantity of thermal energy required to raise temp of 1 g of a substance by 1 degrees c |
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Do substances with higher specific heat capacity take longer to cool? |
Yes |
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What is bond dissociation energy? |
The energy required to break a given chemical bond |
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Why are bond dissociation energies reported as average bond energies? |
The bond dissociation energy of a given bond depends on the types of atoms + bonds in the same molecules. |
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Why does it take more energy to break multiple bonds than single bonds? |
-Multiple bonds are stronger than single bonds -as the number of bonds increases, the bond lengths shortens |
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What can bond energy values be used to calculate? |
Approximate enthaply changes for reactions |
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Why are the bond dissociation energies positive? |
In order for bonds to break, energy must e added (endothermic) |
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Why does making new bonds have a negative /_\H sign? |
Energy is released (exothermic) |
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What is the equation for enthalpy change? |
/_\H = sum of energy required break old bonds (postive values) + Sum of energies released in the formation of new bonds ( negative values) |
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What can you conclude from knowing that C-H, C2H6(g), C2Hc, and CH3Cl all have similar bond energies? |
Molecules with similar bonds act in similar ways |
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What is Hess's Law? |
The enthalpy change in the conversion of reactants to products is the same whether the conversion occurs in one step or several steps |
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Who created Hess's Law? |
Germain Henri Hess |
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What is Hess's law very useful for studying? |
energy changes in chemical reactions that cannot be analyzed using calorimetry (some reactions are too fast/slow) |
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Does the net enthalpy stay the same whether the process occurs in one step vs. many? |
Yes |
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What is the first rule of Hess's law? |
If you reverse a chemical equation, you must reverse the sign on Delta H |
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What is the second rule? |
Whatever you multiply/divide coefficients by, /_\H must be multiplied/divided by the same factor |
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Where does the majority of atmospheric sulfur dioxide gas come from? |
the combustion of fossil fuels containing sulfur impurities |
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What does a formation reaction represent? |
The formation of a compound from its elements |
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What is the standard enthalpy of formation? |
the change in enthalpy that accompanies the formation of ONE MOL of a compound from its elements in their standard states |
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What is standard state? |
the most stable form of a substance under standard conditions (25 degrees Celsius & 100kPa) |
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What are most elements in their standard state? |
solids |
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What are noble gases/diatomic elements in their standard state? |
gases |
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What is the standard state of bromine + mercury? |
liquid |
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What is the standard state for a substance in solution? |
1mol/L |
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What does the degree sign on the symbol H° f indicate? |
the reaction takes place under standard conditions |
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What is the standard enthalpy of formation of an element in its standard state? |
zero |
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Why is a value of zero assigned to an element in its standard state? |
the element is in its most fundamental form at standard conditions |
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How can the enthalpy change for any reaction be calculated? |
by subtracting the sum of the enthalpies of formation of the reactants from the sum of the enthalpies of formation of the products (/_\H° r=SUM of /_\H° products-SUM of /_\H° reactants) |
