Chemical Energetics (A Level Only) | CIE A Level Chemistry Structured Questions 2022

1a3 marks

This question is about the formation of calcium oxide.

Explain the meaning of the term lattice energy.

How did you do?

1b2 marks

The Born- Haber cycle In Fig. 1.1 can be used to determine the lattice enthalpy of calcium oxide.

Steps A-G includes the values for enthalpy changes.

Complete the Born Haber cycle by adding the species present on the two dotted lines.

Include state symbols.

Fig. 1.1

How did you do?

1c3 marks

Name the enthalpy changes for the following steps in the Born-Haber cycle.

Step B .....................................................................
Step D ...................................................................
Step F ...................................................................

How did you do?

1d2 marks

Step C represents the enthalpy change of atomisation of oxygen.

Why is the enthalpy change of atomisation always a positive value?

How did you do?

Did this page help you?

1a7 marks

Potassium sulfide is a reagent used in analytical chemistry and pharmaceutical preparations.

Draw a fully labelled Born-Haber cycle for the formation of solid potassium sulfide from its elements.

Include state symbols for all species involved.

How did you do?

1b

3 marks

Use the data in Table 1.1 to calculate the lattice enthalpy of potassium sulfide, ΔH^θ_latt. Show your working.

Table 1.1

Enthalpy change	Enthalpy change / kJ mol^–1
Formation of potassium sulfide	– 381
1st electron affinity of sulfur	– 200
2nd electron affinity of sulfur	+ 640
Atomisation of sulfur	+ 279
1st ionisation energy of potassium	+ 419
Atomisation of potassium	+ 89

ΔH^θ_latt= ................................. kJ mol^-1

How did you do?

1c2 marks

Explain the difference in values between the first and second electron affinities of sulfur.

How did you do?

Did this page help you?

1a3 marks

Lattice energies are always negative showing that they represent exothermic changes.

i)

Explain what is meant by lattice energy.

[2]

ii)

Explain why lattice energy is an exothermic process.

[1]

Table 5.1

energy change	value / kJ mol^–1
standard enthalpy change of atomisation of potassium	+89
electron affinity of O(g)	–141
electron affinity of O^–(g)	+798
standard enthalpy change of formation of potassium oxide	–361
first ionisation energy of potassium	+418
second ionisation energy of potassium	+3070
first ionisation energy of oxygen	+1310
second ionisation energy of oxygen	+3390
O=O bond energy (diatomic molecule)	+496
O–O bond energy (polyatomic molecule)	+150

How did you do?

1b

4 marks

i)

Use relevant data from Table 5.1 to calculate the lattice energy,

∆ H_{latt}^{ɵ}

, of potassium oxide, K₂O (s).
Show your working.

$∆ H_{latt}^{ɵ}$ , of K₂O (s) = ............................................. kJ mol^–1 [3]

ii)

State how

∆ H_{latt}^{ɵ}

Na₂O (s) differs from

∆ H_{latt}^{ɵ}

K₂O (s).
Indicate this by placing one tick (

✓

) in the appropriate box in Table 5.2.

Table 5.2

$∆ H_{latt}^{ɵ}$ Na₂O (s) is less negative than $∆ H_{latt}^{ɵ}$ K₂O (s)	$∆ H_{latt}^{ɵ}$ Na₂O (s) is the same as $∆ H_{latt}^{ɵ}$ K₂O (s)	$∆ H_{latt}^{ɵ}$ Na₂O (s) is more negative than $∆ H_{latt}^{ɵ}$ K₂O (s)

Explain your answer.

[1]

How did you do?

Did this page help you?

	Download	View
Easy
Medium
Hard

Step	Name of the Enthalpy Change
1
2	Atomisation of potassium
3
4	First ionisation energy of potassium
5
6	Lattice enthalpy of formation

Enthalpy change	Enthalpy change (kJ mol^-1)
ΔH^θ_latt KF	-830
ΔH^θ_hyd K⁺	-351
ΔH^θ_hyd F^–	-504

Enthalpy change	Enthalpy change	Enthalpy change / kJ mol^-1
ΔH^θ_f NaCl	Na (s) + ½Cl₂ (g) → NaCl (s)	-411
ΔH^θ_at Cl	½Cl₂ (g) → Cl (g)	121
ΔH^θ_at Na	Na (s) → Na (g)	108
E_ea Cl	Cl (g) → Cl - (g)	-349
ΔH^θ_ie Na	Na (g) → Na⁺ (g)	496
ΔH^θ_latt NaCl	Na⁺ (g) + Cl^– (g) → NaCl (s)	To be calculated

Enthalpy change	Enthalpy change / kJ mol^-1
Lattice energy of MgO (s)	- 3791
Enthalpy change of atomisation of Mg	148
Enthalpy of atomisation of oxygen	248
Electron affinity of the oxygen atom	-141
Electron affinity of the oxygen anion, O^–	798
First ionisation energy of Mg	736
Enthalpy of formation of MgO	552

CIE A Level Chemistry

Topic Questions

5.1 Chemical Energetics (A Level Only)

Enthalpy Change	Enthalpy Change / kJ mol^-1
Atomisation of aluminium	+326
Atomisation of oxygen	+249
First ionisation energy of aluminium	+578
Second ionisation energy of aluminium	+1817
Third ionisation energy of aluminium	+2745
Electron affinity of O atom	-141
Electron affinity of O^–	+753
Formation of aluminium oxide	-1670

Group 1 ion	Enthalpy of hydration (kJ mol^-1)
Li⁺	-519
Na⁺	-406
K⁺	-321
Rb⁺	-296

Name of enthalpy change	Energy change / kJ mol^-1
Li (s) → Li (g)	+216
Li (g) → Li⁺(g) + e^-	+520
F₂(g) → 2F (g)	+158
F (g) + e^- → F^- (g)	-348
Li (s) + ½F₂(g) → LiF (s)	-594

Name of enthalpy change in solution	Enthalpy change (kJ mol^-1)
Enthalpy of lattice dissociation potassium fluoride	+829
Enthalpy of hydration of potassium ions	-340
Enthalpy of hydration of fluoride ions	-504

standard enthalpy change of formation	–796 kJ mol^–1
standard enthalpy change of atomisation of Ca(s)	+178 kJ mol^–1
electron affinity per mole of chlorine atoms	–349 kJ mol^–1
first ionisation energy of Ca	+590 kJ mol^–1
second ionisation energy of Ca	+1150 kJ mol^–1
standard enthalpy change of atomisation Cl₂ (g)	+244 kJ mol^–1

ΔH^θ_lattMgCl₂(s)	–2526 kJ mol^-1
ΔH^θ_hyd(Mg²⁺(g))	–1890 kJ mol^-1
ΔH^θ_hyd (Cl^–(g))	–398 kJ mol^-1

Name of enthalpy change	Energy change (kJ mol^-1)
Enthalpy of atomisation of magnesium	+150
Second ionisation energy of magnesium	+1450
Enthalpy of formation of magnesium fluoride	-642
Lattice enthalpy of formation of magnesium fluoride	-2493