Lattice Enthalpy

Question 1

How are lattices stable? (2)?

Answer 1

• Strength of the ionic bonds.
• Electrostatic attractions between oppositely-charged ions in the ionic lattice structure.

Question 2

What is lattice enthalpy regarding enthalpy?

Answer 2

The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.

Question 3

What type of reaction is lattice enthalpy?

Answer 3

An exothermic change - negative.

Question 4

How do you measure lattice enthalpy indirectly?

Answer 4

Using an energy cycle called a Born-Haber cycle.

Question 5

How many processes are in route 1 of the Born-Haber cycle?

Answer 5

3.

Question 6

What are the 3 processes in route 1 of the Born-Haber cycle?

Answer 6

1. Formation of gaseous atoms:
   - Changing the elements in their standard states into gaseous atoms.
   - This change is endothermic as it involves bond breaking.
2. Formation of gaseous ions:
   - Changing the gaseous atoms into positive and negative gaseous ions.
   - This change is endothermic.
3. Lattice formation:
   - Changing the gaseous ions into the solid ionic lattice.
   - This is the lattice enthalpy and is exothermic.

Question 7

What is involved in route 2 of the Born-Haber cycles?

Answer 7

Converts the elements in their standard states directly to the ionic lattice, involving the enthalpy change of formation - exothermic.

Question 8

What are the 4 key enthalpy changes? Definitions?

Answer 8

1. The standard enthalpy change of formation: the enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states.
2. The standard enthalpy change of atomisation: the enthalpy change that takes place for the formation of one mole of gaseous atoms from the element in its standard state under standard conditions - endothermic because bonds are broken to form gaseous atoms.
3. The first ionisation energy: the enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions - endothermic because energy is required to overcome the attraction between a negative electron and the positive nucleus.
4. The first electron affinity: the enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions - exothermic because the electron being added is attracted in towards the nucleus.

Question 9

What is the difference between ionisation energies and electron affinities?

Answer 9

Ionisation energy measures the energy to gain electrons but electron affinities measures the energy to gain electrons.

Question 10

What are second electron affinities? How do they differ to first ionisation energies?

Answer 10

When a second electron is being gained by a negative ion, which repels the electron away. So, energy must be put in to force the negatively-charged electron onto the negative ion:

• First EA: O (g) + e- = O- (g).
• Second EA: O- (g) + e- = O2- (g).