Definitions

Question 1

Lattice Enthalpy

Answer 1

The enthalpy change when one mole of an ionic compound is converted to gaseous ions

Question 2

Standard enthalpy change of formation

Answer 2

The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions

Question 3

Standard enthalpy change of atomisation

Answer 3

The enthalpy change when one mole of gaseous atoms is formed from the element in its standard state

Question 4

Standard bond dissociation enthalpy

Answer 4

The enthalpy change required to break one mole of a covalent bond, everything being in the gas state

Question 5

First ionisation energy

Answer 5

The enthalpy change accompanying the removal of one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

Question 6

Second ionisation energy

Answer 6

The enthalpy change accompanying the removal of one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

Question 7

First electron affinity

Answer 7

The enthalpy change when one mole of gaseous atoms is converted into gaseous ions with a single negative charge

Question 8

Second electron affinity

Answer 8

The enthalpy change when one mole of gaseous 1- ions is converted into one mole of gaseous ions with a double negative charge

Question 9

Enthalpy of solution

Answer 9

The enthalpy change when one mole of a solute dissolves in water

Question 10

Enthalpy of hydration

Answer 10

The enthalpy change when one mole of gaseous ions is converted to one mole of aqueous ions

Question 11

Spontaneous changes

Answer 11

Changes that have a natural tendency to occur without any external help

Question 12

Entropy (S)

Answer 12

A ‘measure of disorder (randomness) of a system
- always a positive value as all substances possess some degree of disorder because particles are always in constant motion

Question 13

The Second Law of Thermodynamics

Answer 13

“The sum of the entropy changes for a chemical system and its surroundings must be positive for a process to be spontaneous (feasible)

Question 14

Standard entropy change

Answer 14

The entropy change per mole for conversion of reactants in their standard states into products in their standard states, at a stated temperature

Question 15

Activation energy

Answer 15

The minimum amount of energy reactant particles must possess in order for collisions to result in a reaction

Question 16

Rate of reaction

Answer 16

The change in concentration of a reactant or product with respect to time

Question 17

The order of a reaction (with respect to a particular reactant)

Answer 17

The power to which the concentration of a reactant is raised in the rate equation

Question 18

The overall order of reaction

Answer 18

The sum of the powers to which the concentration terms are raised in the rate equation i.e x+y

Question 19

The rate constant

Answer 19

The proportionality constant which links the rate of the reaction to the concentrations in the rate equation

Question 20

Rate determining step

Answer 20

The slowest step in the mechanism of a reaction

Question 21

Activation energy Ea (AS)

Answer 21

The minimum amount of energy required for a reaction to occur

Question 22

Catalyst (AS)

Answer 22

A substance which increases the rate of a chemical reaction but does not get used up

Question 23

Homogeneous

Answer 23

That catalyst is in the same physical state as the reactants and products

Question 24

Heterogeneous

Answer 24

The catalyst is not in the same physical state as the reactants and products