OCR A Level Chemistry

Topic Questions

A LevelChemistryOCRTopic Questions5. Physical Chemistry & Transition Elements (A Level Only)5.4 Thermodynamics

5.4 Thermodynamics

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11 mark

The lattice enthalpy of calcium chloride can be calculated using three of the enthalpy changes below.

Which enthalpy change is not required?

  • Enthalpy change of solution of calcium chloride

  • Enthalpy change of hydration of Cl– ions

  • Enthalpy change of formation of calcium chloride

  • Enthalpy change of hydration of Ca2+ ions

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21 mark

Ammonia is produced according to the following gas-phase synthesis:

N2 (g) + 3H2 (g) ⇌ 2NH3 (g)

Thermodynamic data for the components of this equilibrium are:

Substance 

N2 (g)

H2 (g)

NH3 (g) 

SӨ (J K-1 mol-1)

191.5

130.6

192.5

What is the standard entropy change for this reaction?

  • -129.6 J K-1 mol-1

  • -198.3 J K-1 mol-1

  • 198.3 J K-1 mol-1

  • 514.6 J K-1 mol-1

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31 mark

Which of the following is the correct equation for Gibbs free energy?

  • ΔG = ΔH - TΔS

  • ΔG = ΔH + TΔS

  • ΔG =  TΔS - ΔH

  • ΔG = ΔS + TΔH

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41 mark

Which of the following best explains why lithium oxide has a much larger lattice enthalpy than potassium oxide?

  • Lithium ions have a greater charge than potassium ions

  • Potassium oxide has a greater Mr than lithium oxide

  • Potassium ions have a greater charge than lithium ions

  • Lithium ions have a smaller ionic radius than potassium ions

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51 mark

Which of the following represents the first electron affinity of oxygen?

  • O (g) + e- → O- (g)

  • 2O (g) + 2e- → 2O- (g)

  • O (g) + 2e- → O2- (g)

  • O- (g) → O (g) + e-

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11 mark

What is the correct equation for the given term?

  • increment H subscript f superscript theta = 2Na (s) + Cl2 (g) → 2NaCl (s)

  • E(Cl-Cl) = Cl2 (g) → 2Cl (g)

  • increment H subscript a t end subscript superscript theta = Cl2 (g) → 2Cl (g)

  • increment H subscript L E end subscript superscript theta  = Na+ (s) + Cl- (g) → NaCl (s)

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21 mark

Which is the correct order for increasing lattice enthalpy?

  • LiCl < CsF < LiF < CaO

  • CaO < LiF < LiCl < CsF

  • CsF < LiCl < LiF < CaO

  • CsF < LiF < LiCl < CaO

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31 mark

Standard enthalpy change data for barium chloride is given below.

Enthalpy change

 (kJ mol-1)

Enthalpy of atomisation of barium

+180

Enthalpy of atomisation of chlorine

+122

Enthalpy of formation of barium chloride

-859

First ionisation energy of barium

+503

Second ionisation energy of barium

+965

Lattice enthalpy of formation of barium chloride

-2056

 

Which of the following statements is/are correct?

  1. The electron affinity for chlorine is -695 kJ mol-1.
  2. The bond enthalpy for chlorine is +244 kJ mol-1.
  3. The lattice enthalpy for barium bromide would be less exothermic than barium chloride.

  • 1, 2 and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

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41 mark

Four different chemical reactions are described.

  • Reaction A: K (g) → 2L (g)                           exothermic
  • Reaction B: M (g) + N (g) → P (g)                endothermic
  • Reaction C: 2H (g) + I (g) → J (g)                exothermic
  • Reaction D: E (s) → F (s) + G (g)                endothermic

Which row has correct descriptions for the entropy change and feasibility of the reaction?

Reaction

Entropy change

Feasibility

A

Most positive

Always feasible

B

Second most negative

Feasible above a certain temperature

C

Most negative

Feasible below a certain temperature

D

Second most positive

Never feasible

 

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51 mark

Iron can be extracted from iron(III) oxide in a reduction reaction. The enthalpy and entropy changes of this reaction are +492.7 kJ mol-1 and 542.6 J K-1 mol-1.

At which temperature does this reaction become feasible?

  • 635 oC

  • 908 oC

  • -272 K

  • 828 oC

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11 mark

Ethene is produced according to the following gas-phase synthesis:

2C (s)  + 2H2 (g) → C2H4 (g) 

Thermodynamic data for the components of this equilibrium are:

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What is the free energy change for this reaction at 330 K?

  • + 18202 kJ mol-1

  • + 33.83 kJ mol-1

  • + 70.15 kJ mol-1

  • -18098 kJ mol-1

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21 mark

Using the information in the table to answer the question.

Ion Value (kJ mol-1)
ΔHӨlatt CaF2 -2651
ΔHӨhyd Ca2+ -1616
ΔHӨhyd F-  -504

Which of the following is the correct value for the enthalpy change of solution, ΔHӨsol, of calcium fluoride, CaF2.

  • +531 kJ mol-1

  • -5275 kJ mol-1

  • +27 kJ mol-1

  • -1589 kJ mol-1

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31 mark

Which of the following conditions will mean a reaction is never feasible?

  ΔH ΔS Temperature
A Negative Positive High
B Positive Negative High
C Negative Negative Low
D Positive Positive High

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41 mark

Which of the following ionic compounds has the greatest lattice enthalpy?

  • Potassium chloride

  • Calcium bromide

  • Beryllium oxide

  • Silver bromide

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51 mark

Which of the following changes is not endothermic?

  • K (g) → K+ (g) + e-

  • Cl (g) + e- → Cl- (g)

  • Ca (s) → Ca (g)

  • O- (g) + e- → O2- (g)

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