5.4 - Lattice Enthalpy

Question 1

Define first electron affinity

Answer 1

enthalpy change when 1 electron added to each atom in 1 mol of gaseous atoms to form 1 mol of gaseous 1- ions

Question 2

Define standard enthalpy change of atomisation

Answer 2

enthalpy change when 1 mol of gaseous atoms formed from the element in its standard state under standard conditions
(endothermic process: bonds broken)

Question 3

Define lattice enthalpy

Answer 3

enthalpy change when 1 mol of ionic lattice is formed from its gaseous ions under standard conditions

Question 4

Define standard enthalpy change of formation

Answer 4

enthalpy change when 1 mol of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states

Question 5

Define 1st ionisation energy

Answer 5

enthalpy change when 1 electron is removed from each atom in 1 mol of gaseous atoms to form 1 mol of gaseous 1+ ions

Question 6

Why are ionisation energies endothermic?

Answer 6

energy required to overcome attraction between - electron and + nucleus

Question 7

Electron affinities, exo or endo?

Answer 7

1st: exo (electron added attracted towards nucleus)
2nd or more: endo (negative ion repels added electron)

Question 8

Define standard enthalpy change of solution

Answer 8

enthalpy change when 1 mole of a solute dissolves in water
(can be endo/exo)

Question 9

Define enthalpy change of hydration

Answer 9

enthalpy change when 1 mol of gaseous ions dissolves in water forming 1 mol of aqueous ions under standard conditions

Question 10

Factors affecting lattice enthalpy

Answer 10

smaller ionic radius:
- electrostatic attraction between closely packed ions increases
- higher charge density
- higher MP so more energy required to overcome attraction
- LE increases (more exothermic)

greater ionic charge:
- electrostatic attraction between ions increases
- greater charge density
- LE increases (more exothermic)

NB: both have converse too, and specify which ions attraction is between

Question 11

Factors affecting hydration

Answer 11

smaller ionic radius:
- stronger attraction between ions and water
- more negative/exothermic hydration

greater ionic charge:
- stronger attraction with water molecules
- more exothermic

NB: both have converse too, and specify which ion/s

Question 12

When is the enthalpy change of solution endothermic?

Answer 12

when LE>hydration/s

Question 13

How would using a larger volume of water affect:
- temp change
- enthalpy change of solution of _____

Answer 13

• decrease temp change as heat spread over larger volume (specify new temp change)
• enthalpy of solution stays same as same energy released per mole of ____