Energetics

Question 1

How to calculate heat energy released (q)

Answer 1

q = mcΔT

Question 2

Specific heat capacity

Answer 2

The heat required to increase the temperature of 1g of the substance by 1oC

Question 3

Exothermic

Answer 3

Chemical energy is converted into heat energy and the temperature of the system rises

Question 4

Endothermic

Answer 4

Heat energy is converted to chemical energy and the temperature of the system falls

Question 5

Enthalpy, H

Answer 5

The chemical energy in the system at constant pressure that can be converted into heat

Question 6

Hess’s law

Answer 6

The enthalpy change for any reaction is independent of the route taken from reactants to products

Question 7

Standard enthalpy of formation

Answer 7

Enthalpy change when 1 mole of a substance is formed from its constituent elements in their standard states

Question 8

Units of enthalpy

Answer 8

kJ mol^-1

Question 9

Standard enthalpy of reaction

Answer 9

Enthalpy change when the number of moles of the substances in the equation as written react

Question 10

Standard enthalpy of combustion

Answer 10

Enthalpy change when 1 mol of the substance undergoes complete combustion in excess oxygen

Question 11

Standard enthalpy of neutralisation

Answer 11

Enthalpy change when 1 mol of water is produced by the neutralisation of a solution of an acid by excess base

Question 12

Standard enthalpy of atomisation

Answer 12

Enthalpy change when 1 mol of gaseous atoms is formed from an element in its standard state

Question 13

Bond dissociation enthalpy

Answer 13

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

Question 14

Lattice enthalpy of formation

Answer 14

Enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in the gas phase (note: you can also have lattice enthalpy of dissociation, when the ionic compound is split into its constituent ions)

Question 15

Enthalpy of solution

Answer 15

Enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so the dissolved ions are well separated and don’t interact

Question 16

Hydration enthalpy

Answer 16

Enthalpy change when one mole of gaseous ions become hydrated (dissolved in water)

Question 17

First electron affinity

Answer 17

Enthalpy change when one mole of gaseous atoms gains one electron per atom to produce gaseous 1- ions

Question 18

First ionisation enthalpy

Answer 18

The enthalpy change when one mole of gaseous atoms loses one electron per atom to produce gaseous 1+ ions

Question 19

Second ionisation energy

Answer 19

When one mole of gaseous 2+ ions is produced from one mole of 1+ ions