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

Thermodynamics (OCR A Level Chemistry)

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5.4 Thermodynamics

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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

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:

cb14c434-c65b-48df-8a53-9aeca4eac391

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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    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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