5.2.1 - Lattice enthalpy

Question 1

Lattice enthalpy

Answer 1

Enthalpy change when one mole of an ionic compound is formed from the gaseous ions under standard conditions

Question 2

Is lattice enthalpy exo/endothermic

Answer 2

Exothermic

Question 3

What does lattice enthalpy measure

Answer 3

Ionic bond strength

Question 4

Why is breaking ionic lattice endo

Answer 4

Energy is required to overcome ionic bonds

Stronger bonds –> more +ve

Question 5

General formula for BHC w/ formation

Answer 5

Formation 
Atomisation ^
Atomisation ^
1st IE ^
1st EA 
LE

Question 6

Enthalpy of atomisation

Answer 6

Standard enthalpy change when one mole of gaseous atoms is formed from its elements in their standard states

Always +ve

Question 7

Enthalpy of 1st electron affinity

Answer 7

Enthalpy change of adding one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

Exothermic

Question 8

Enthalpy of 2nd electron affinity

Answer 8

Enthalpy change of adding one electron to each ion in one mole of gaseous ions to form one mole of gaseous 2- ions

Endothermic

Question 9

Factors affecting LE

Answer 9

Ionic size

Ionic charge

Question 10

How does ionic size affect LE

Answer 10

Smaller ions can pack together more closely in a lattice and attract each other more strongly
Leads to a more exothermic LE

Question 11

How does ionic charge affect LE

Answer 11

Ions w/ higher charges attract each other more strongly

As the charge on the cations increase, LE becomes more exo

Question 12

When is enthalpy of hydration/solution used

Answer 12

Ions that contain more than one element eg. NO3-, CO3^2-, SO4^2- and salts

Question 13

Enthalpy of solution

Answer 13

Enthalpy change that takes place when 1 mole of an ionic compound dissolves completely in water
Can be endo/exothermic

Question 14

Enthalpy of hydration

Answer 14

Enthalpy change that takes place when 1 mole of gaseous ions dissolves in water to form 1 mole of aq ions
Always exo

Question 15

Factors affecting Enthalpy of hydration

Answer 15

Ionic size

Ionic charge

Question 16

How does ionic size affect enthalpy of hydration

Answer 16

Smaller ions have more exothermic enthalpies of hydration

Grreater charge density means stronger bonding w/ water

Question 17

How does ionic charge afffect enthalpy of hydration

Answer 17

Higher charge ions have more exothermic enthalpies of hydration due to stronger bonds w/ H2O due to dipoles

Question 18

General formula for BHC w/ hydration

Answer 18

LE
Hydration
Hydration
Solution ^

Question 19

How does LE change across a period

Answer 19

Ionic charge increases
Ionic radius decreases
Stronger ionic bonds due to increased attraction between ions so w/ more -ve LE
Sronger bonds w/ H2O –> more - ve hydration enthalpies

Question 20

How does LE change down a group

Answer 20

Atomic charge stays the same
Ionic radius increases
Charge density decreases so weaker ionic bonds due to weaker forces of attraction –> less -ve LE
Weaker bonds w/ H2O due to weaker dipoles –> less -ve hydration enthalpies

Question 21

Why is the 2nd IE more endo than the 1st

Answer 21

X^+ is smaller than X

Greater nuclear attraction

Question 22

Why is the second EA +ve

Answer 22

More energy is required to overcome the repulsion between X^- and the electron

Question 23

Why is the first EA -ve

Answer 23

Involves electron experiencing attraction to the nucleus