Chapter 22.1 - Lattice enthalpy

Question 1

What is lattice enthalpy?

Answer 1

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

Question 2

What is the standard enthalpy change of formation?

Answer 2

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

Question 3

What is the standard enthalpy change of atomisation?

Answer 3

The enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state

Question 4

What is the first ionisation energy?

Answer 4

The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions

Question 5

What is the first electron affinity?

Answer 5

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

Question 6

What type of change is lattice enthalpy? + what is the value for enthalpy change

Answer 6

Exothermic change
- Value for enthalpy change is always negative

Question 7

What are the three different processes in route 1?

Answer 7

1. Formation of gaseous atoms
2. Formation of gaseous ions
3. Lattice formation

Question 8

Describe what happens in the formation of gaseous atoms

Answer 8

• Changing the elements in their standard states into gaseous atoms
• The change is endothermic as it involves bond breaking

Question 9

Describe what happens in the formation of gaseous ions

Answer 9

• Changing the gaseous atoms into positive and negative gaseous ions
• The change is endothermic overall

Question 10

Describe what happens in lattice formation

Answer 10

• Changing the gaseous ions into the solid ionic lattice
• This is the lattice enthalpy and is exothermic

Question 11

What is the process in route 2?

Answer 11

• Conversion of the elements in their standard states directly to the ionic lattice
• One enthalpy change: enthalpy change of formation - exothermic

Question 12

What type of reaction is atomisation?

Answer 12

• Endothermic as bonds are broken to form gaseous atoms
• If the element is a gas in its standard state, the bond enthalpy is of the bond being broken

Question 13

Why are ionisation energies endothermic?

Answer 13

This is because energy is required to overcome the attraction between a negative electron and the positive nucleus

Question 14

What is meant when electron affinity is the opposite of ionisation energy?

Answer 14

• Electron affinity measures the energy to gain electrons
• Ionisation energy measures the energy to lose electrons

Question 15

Why are first electron affinities exothermic?

Answer 15

Because the electron being added is attracted in towards the nucleus

Question 16

Why are second electron affinities endothermic?

Answer 16

Because a second electron is being gained by a negative ion, which repels the electron away
- Energy must be put in to force the negatively-charged electron onto the negative ion