Thermodynamics

Question 1

Enthalpy of formation

Answer 1

Enthalpy change when one mole of a substance is formed from its constituent elements in their standard states

Question 2

Enthalpy of combustion

Answer 2

Enthalpy change when one mole of a substance undergoes combustion under oxygen in standard states

Question 3

Enthalpy of neutralisation

Answer 3

Enthalpy change when one mole of water is formed in a reaction between an acid and an alkali under standard conditions

Question 4

Ionization energy

Answer 4

Enthalpy change when one atom in one mole of gaseous atoms loses one electron to form one mole of gaseous ion

Question 5

Electron affinity

Answer 5

Enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous ions

Question 6

Enthalpy of atomisation

Answer 6

Enthalpy change when one mole of gaseous atoms is produced from an element in its standard state

Question 7

Hydration enthalpy

Answer 7

Enthalpy change when one mole of gaseous ion becomes hydrated

Question 8

Enthalpy of solution

Answer 8

Enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough, so dissolved ions are separated and do not come into contact

Question 9

Bond dissociation Enthalpy

Answer 9

Enthalpy change when one mole of covalent bonds is broken in the gaseous state

Question 10

Lattice enthalpy of formation

Answer 10

Enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in the gas phase

Question 11

Lattice Enthalpy of dissociation

Answer 11

Enthalpy change when one mole of a solid ionic compound is broken up into its constituent ions in the gas phase

Question 12

Enthalpy of vaporization

Answer 12

Enthalpy change when one mole of a liquid is turned into a gas

Question 13

Enthalpy of fusion

Answer 13

Enthalpy change when one mole of a solid is turned into a liquid

Question 14

how do you work out enthalpy of solution

Answer 14

enthalpy of solution = lattice enthalpy of formation - enthalpy of hydration.
measured in kjmol-1

Question 15

what is a born haber cycle

Answer 15

a cycle that shows all the enthalpy changes to form an ionic compound.

Question 16

what are the stages of a born haber cycle

Answer 16

1. enthalpy of formation
2. enthalpy of atomisation
3. ionisation energy
4. electron affinity
5. lattice enthalpy of formation

Question 17

how to work out enthalpy of formation

Answer 17

enthalpy of formation = sum of all the other enthalpy values. measured in kjmol-1

Question 18

what do the arrows in a born haber cycle represent

Answer 18

arrows going down are exothermic reactions, and arrows going up are endothermic reactions.

Question 19

what is entropy

Answer 19

a measure of disorder in a system, the greater the disorder the greater the entropy. measured in J mol-1 K-1

Question 20

trend of entropy between states

Answer 20

going from a solid to a liquid to a gas, increases entropy as disorder increases.

Question 21

what are the factors which increase entropy

Answer 21

melting
boiling
dissolving
increasing number of particles
increasing temperature

Question 22

how do you calculate entropy change

Answer 22

∆s = sum of entropy of products - sum of entropy of reactants

Question 23

what is Gibbs free energy

Answer 23

a term which combines the effect of entropy and enthalpy together

Question 24

how do you work out Gibbs free energy

Answer 24

∆G = ∆H - T∆s
measured in KJ mol-1

Question 25

what is feasibility mean and when is a system feasible

Answer 25

how likely a reaction is to take place
∆G must be zero or negative for a reaction to be feasible.