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 are the main features of lattice enthalpy?

Answer 2

• exothermic (-ve sign)
• measure of ionic bond strength

Question 3

What is the standard enthalpy of atomisation?

Answer 3

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

Question 4

What is the first ionisation energy in enthalpy terms?

Answer 4

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

Question 5

What is the second ionisation energy in terms of enthalpy change?

Answer 5

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 6

What is the first electron affinity?

Answer 6

The enthalpy change accompanying the addition of one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

Question 7

How does ionic size affect lattice enthalpy?

Answer 7

As ionic radius increases:
- attraction between ions decrease
- lattice enthalpy is less negative
- so melting point decreases

Question 8

How does ionic charge affect lattice enthalpy?

Answer 8

As ionic charge increases:
- attraction between ions increases
- lattice enthalpy becomes more negative
- so melting point increases

Question 9

How can you use lattice enthalpies to predict melting points?

Answer 9

The more negative the lattice energy, the higher the melting point