Enthalpy

Question 1

Standard enthalpy of formation

Answer 1

Enthalpy change when 1 mol of a substance is formed from its elements in their standard states at 100kPa pressure and a state temperature, usually 298k

Question 2

Standard enthalpy of reaction

Answer 2

The enthalpy change when the number of molecules of the substances in the equation as written react under standard conditions of 100kPa pressure and a stated temperature usually 298K

Question 3

Standard enthalpy of combustion

Answer 3

The enthalpy change when one mole of the substance is burnt in excess oxygen under standard conditions of 100kPa pressure and a stated temperature usually 298K

Question 4

Standard enthalpy of neutralisation

Answer 4

The enthalpy change when one mole of water is produced by the neutralisation of an acid by excess base under standard conditions

Question 5

Standard enthalpy of atomisation

Answer 5

The enthalpy change when one mole of of gaseous atoms is formed from an element in its standard state at 100kPa and 298K

Question 6

Bond enthalpy

Answer 6

The enthalpy change when one mol of a bond is broken in a gaseous molecule

Question 7

Mean bond enthalpy

Answer 7

The average enthalpy change when one mole of a bond Is broken across a variety of compounds in its gaseous state

Question 8

Lattice energy

Answer 8

The energy change when one mole of the solid is formed from its constituent gaseous ions that start infinitely far apart. It is always exothermic

Question 9

First electron affinity

Answer 9

The energy change when 1 mole of gaseous 1- ions are formed from 1 mol of gaseous atoms by the addition of one mole of electrons

Always exothermic

Question 10

Second electron affinity

Answer 10

The energy change when one mole of electrons is added to gaseous one mole of 1- ions forming one mole of 2- ions

Always endothermic

Question 11

Enthalpy of solution

Answer 11

The enthalpy change when 1 mol of the solid is dissolved in sufficient solvent to give an infinitely dilute solution

Question 12

Hydration enthalpy

Answer 12

The enthalpy change when one mole of gaseous ions is dissolved in sufficient solvent to give an infinitely dilute solution

Question 13

Dissolving

Answer 13

The magnitude of the hydration enthalpy is larger than the magnitude of the lattice enthalpy

Question 14

Enthalpy of neutralisation of a weak acid

Answer 14

The acid must first dissociate.
This is endothermic therefore the value of the enthalpy of neutralisation is less exothermic than the enthalpy of neutralisation of a strong acid