Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
34 Cards in this Set
- Front
- Back
|
what is enthalpy of formaton |
the enthaply change when one mole of a substance isfromed from its constituent elements with all substances in their standard states under standard conditions |
|
|
what is enthalpy of combustion |
the enthalpy change when one mole of a substance undegoes complete combustion in oxygen to form carbon dioxide and water with all substances in their standard states undeer standard conditions |
|
|
what is enthaly of neutalisation |
the enthalpy chaange when one mole of water is formed in a reaction between an acid and an alkali under standard conditions |
|
|
what is ionisation enthalpy |
the enthalpy change when each atom in one mole of gaseous atoms loeses one electron to form one mole of gaseous 1+ ions |
|
|
what is eectron affinity |
enthalpy change when each atom in one mole of gaseous atoms gains an electron to form one mole of gaseous 1- ions |
|
|
what is enthalpy of atomisation |
enthalpy change when one mole of gaseous atoms is produced from an element in its standard state |
|
|
what is enthalpy of hydration |
enthalpy change when one mole of gaseous ions become hydrated ( dissolved in water) |
|
|
what is enthalpy of soluton |
enthalpy change when one mole of an ionic solid is dissolved so tat the dissolved ions are well separated and do not interact with each other |
|
|
what is bond dissociation enthalpy |
enthalpy change when one mole of colvalent bonds is broken in the gaseous state |
|
|
what is lattice enthalpy of formation |
enthlalpy change when one mole of an ionic solid compounf iss formed its constituent ions in the gas phase |
|
|
what is lattice enthalpy of dissociation |
enthalpy change when one mole of a solid ionic compound is broken up into its constituent ions in the gas phase |
|
|
what is enthalpy of vapourisation |
enthalpy change when one mole of a liquid is turned into a gas |
|
|
what is enthalpy of fusion |
enthalpy change when one mole of a s olid is turned into a liquid |
|
|
what does lattice enthalpy represent |
the enthalpy change when the ions in one mole of an ionic solid compound are broken apart or brought together |
|
|
what does lattice enthalpy indicate |
the strength of the ionic bondin the greater the magnitude of the lattice enthalpy the stronger the bonding |
|
|
how can we measure lattice enthalpy |
-using born-harbour cycles -a born harbour cycle includes al the enthalpy changes i the formation of an ionic compound |
|
|
Find the lattice enthalpy of formation of calcium oxide using a Born-Haber cycle and these enthalpy changes:1st ionisation enthalpy of calcium = +590 kJ mol-1 atomisation enthalpy of calcium = +193 kJ mol-12nd ionisation enthalpy of calcium = +1150 kJ mol-1 atomisation enthalpy of oxygen = +248 kJ mol-11st electron affinity of oxygen = –142 kJ mol-1 enthalpy of formation of calcium oxide = –635 kJ mol-12nd electron affinity of oxygen = +844 kJ mol |
|
|
|
how is experimental and theoretical lattice enthalpy calculated |
experimental- born-harbour cycle theoretical-by a theoretical equation that considers the size chage aand arrangement of ions in the lattice.it is assumed that the structure is perfectly ionic |
|
|
why might the structure not be perfectly ionic |
•There is often some distortion of the ions in an ionic compounds (i.e. they are polarised) – this means that the ions are not perfectly spherical. If there is a lot of distortion then the ions are said to have some covalent character. This does not mean that the compound is covalent – it is still ionic but the ions are not perfectly spherical. • Positive ions (cations) that are small and/or highly charged are very good at distorting (i.e. they are very good at polarising) negative ions. • Negative ions (anions) that are large and/or highly charged are easier to distort (i.e they are polarisable). • Ionic compounds that have some covalent character often have low solubility in water (or are insoluble) and their melting points and electrical conductivity may not be as high as expected |
|
|
what does the difference between the experimental and theoretical value indicate |
the amount of covalent character. the bigger the difference the more covalent character |
|
|
what is entropy |
-entropy is a disorder.the more disordered something is the greater the entropy -it is measured in j mol-1 k-1 -gases have the most entropy whereas solids have the least entropy this is because the particles in a solid are movig rapidly and randoml whereas in a solid the particles vibrate in a fixed position |
|
|
how does the entropy of substance vary wwith temperature |
-The 3rd law of thermodynamics states that the entropy of a substance is zero (or close to zero) at absolute zero and increases with temperature. - The higher the temperature, the faster the particles vibrate/move and so the greater the entropy (disorder) |
|
|
how does the enropy of different substances compare |
• The more ordered the structure the lower the entropy. • Structures like diamond and graphite are very highly structured and so have very low entropy |
|
|
how to calculate entropy change of a reaction |
change in entropy = [SUM Sproducts] – [SUM Sreactants] |
|
|
what is gibbs free energy change |
combines enthalpy change and entropy change |
|
|
what is the equation for gibbs free energy |
delta G =delta H - TdeltaS |
|
|
is an decrease in enthalpy but an increase in entropy more favourable |
yes |
|
|
how is a reaction feasible |
if the gibbs free energy change is less than or equal to zero |
|
|
wha does feasible mean |
The term feasible means that a reaction can take place. If it is not feasible then it cannot take place |
|
|
whaat does feasibility depend on |
depends on temperature, and reactions are often feasible at one temperature but not at another. The point at which a reaction switches from being feasible to not feasible is when ∆G = 0 |
|
|
why might a reaction that is feasible not take place |
the reaction has a high activation energy |
|
|
what does spontaneous mean |
The term spontaneous is sometimes used in place of feasible. It has the same meaning in this context, meaning that a reaction is thermodynamically possible (but does not mean that it will actually happen). The term spontaneous is a little misleading and the term feasible better describes the situation |
|
|
how does temperature affect feasibility |
|
|
|
how do changes in state affect feasibility |
• Below the melting point of a substance, melting is not feasible as ∆G is positive, but at the melting point it ∆G = 0 and so melting becomes feasible and the substance melts. • In a similar way, below the boiling point of a substance, boiling is not feasible as ∆G is positive, but at the boiling point it ∆G = 0 and so boiling becomes feasible and the substance boils |
