Topic 13

Question 1

Lattice energy

Answer 1

The energy change when 1 mole of an ionic solid is formed from its gaseous ions
Exothermic

Question 2

Enthalpy change of atomisation

Answer 2

Enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state
Endothermic

Question 3

1st electron affinity

Answer 3

The enthalpy change when each atom in 1 mole of gaseous atoms of an element gains 1 electron to form 1 mole of gaseous 1- ions
Exothermic

Question 4

2nd electron affinity

Answer 4

The enthalpy change when each ion in 1 mole of gaseous 1- ions gains 1 electron to form 1 mole of gaseous 2- ions
Endothermic

Question 5

1st ionisation energy

Answer 5

The enthalpy change when each atom in 1 mole of gaseous atoms of an element loses 1 electron to form 1 mole of gaseous 1+ ions
Endothermic

Question 6

Enthalpy change of solution

Answer 6

The enthalpy change when 1 mole of an ionic solid dissolves in water to form an indefinitely dilute solution
Either endo/exo

Question 7

Enthalpy change of hydration

Answer 7

The enthalpy change when 1 mole of gaseous ions is hydrated by water to form an indefinitely dilute solution
Exothermic

Question 8

Cations in a lattice with distortion

Answer 8

Highest polarising power when
Small
Highly charged

Pull electrons of anion towards itself

Question 9

Anions in a lattice with distortion

Answer 9

Highest polarizability when
Large
Highly charged

Electrons pulled away towards cation

Question 10

Experimental vs theoretical lattice energy for LiI

Answer 10

The experimental value is more exothermic than the theoretical
The theoretical model is based on pure ionic bonding
There is a degree of covalency in LiI
Due to polarisation of the iodide ions

Question 11

Lattice energy of MgO vs MgS

Answer 11

Lattice energy of MgO is more exothermic
S2- and O2- ions have the same charge
O2- smaller than S2-
So O2- charge density smaller
O2- forms greater electrostatic attractions with Mg2+
Therefore forms stronger ionic bonds

Question 12

Entropy

Answer 12

Measure of the disorder of a system

Question 13

Entropy increases when

Answer 13

There are more ways to arrange the energy

Moles of gasses increases eg. 5 moles of gas forms from 3 moles of gas.
Solid to liquid. Liquid has more disorder.
Dissolving
Exothermic reaction

Question 14

ΔS system

Answer 14

ΔS products - ΔS reactants

Entropy change in a reaction

Question 15

ΔS total

Answer 15

ΔS system + ΔS surroundings

Must be positive for reaction to be feasible

Question 16

ΔS surroundings

Answer 16

• ΔH / T

Question 17

ΔG

Answer 17

ΔH - TΔS

Must be negative for a reaction to be feasible

Question 18

How feasibility of reaction changes as temperature increases

Answer 18

Eg.
Less feasible as temperature increases, becomes not feasible
Because ΔG becomes more positive
Because magnitude of TΔS increases and -TΔS is positive

Question 19

What is a solvation shell

Answer 19

A group of water molecules that surround an ion, forming bonds with it

Question 20

Why can an endothermic reaction be feasible?

Answer 20

Entropy of surroundings is negative
Entropy of system is positive
Increase in entropy of system outweighs decrease in entropy of surroundings
So total entropy change is positive

Question 21

What happens to the volume of a solution when solid is dissolved in it?

Answer 21

The volume decreases because water molecules are more tightly arranged (clustered around the ions)

Question 22

What is the relationship between G and K

Answer 22

G = -RT lnK

Question 23

If the S system is negative

Answer 23

There is less ways to arrange the energy so the entropy decreases

Question 24

If the S surroundings is positive

Answer 24

The reaction is exothermic , so heat energy is released, so the kinetic energy and movement of molecules increases