A2.4 Lattice Enthalpy

Question 1

^atH

Answer 1

Atomisation of metal and non metal

Endothermic always

Breaking bonds

Na(s) ——> Na(g)

1/2 Cl2 (g) ——> Cl (g)

Question 2

^IEH

Answer 2

Ionisation of metal

Question 3

^eaH

Answer 3

Electron affinity of non metal

Cl(g) + e——> Cl- (g)

First is Exo
Second is endo

Question 4

^LEH

Answer 4

Lattice enthalpy is the formation of one more of ionic lattice from gaseous ions

Question 5

^fH =

Answer 5

All the others added

Question 6

Trends in lattice enthalpy - ionic radius

Answer 6

Ionic radius increases

Attraction between ions decreases

Lattice enthalpy less negative

Mp decreases

Question 7

Trends in lattice enthalpy - ionic charge

Answer 7

Ionic charge increases

Attraction between ions increases

Lattice enthalpy more negative

Mp increases

Question 8

^solH

Answer 8

Enthalpy change when one mole of solute is dissolved in water

NaCl(s) + aq ——> Na+ (aq) + Cl- (aq)

Question 9

Enthalpy of hydration

Answer 9

Enthalpy change for dissolving of one mole of gaseous ions in water to form one mole of aqueous ions

F (g) + aq —-> F- (aq)

Always Exo

Question 10

Equation for enthalpy of solution

Answer 10

^solH + ^LEH = ^hydH

Question 11

If ^solH is endo

Answer 11

Arrow points up on right

Question 12

If ^solH is Exo

Answer 12

Arrow points down on left

Question 13

Trends in hydration enthalpy - ionic radius

Answer 13

Ionic radius increase

Attraction between ion and water molecules decrease

Weaker ion-dipole attraction

Hydration enthalpy less negative

Question 14

Trends in hydration enthalpy - ionic charge

Answer 14

Ionic charge increase

Attraction between ions and water molecule increases

Stronger ion-dipole attraction

Hydration enthalpy becomes more negative

Question 15

Why is the second electron affinity more positive

Answer 15

Anion and electron both negative

Energy needed to overcome repulsion