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International A LevelChemistryEdexcelExam Questions4: Rates, Equilibria and Further Organic Chemistry4.2 Entropy

Entropy (Edexcel International A Level Chemistry)

Exam Questions

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4.2 Entropy

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4.2 Entropy

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11 mark

Which of these has the highest standard molar entropy at 298 K and 1 atm pressure?

  • carbon dioxide, CO2

  • copper, Cu

  • ethanol, C2H5OH

  • hydrogen, H2

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11 mark

Which of these gases would have the greatest standard molar entropy?

  • NH3

  • H2

  • N2

  • SO2

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2
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What is the standard entropy change of the system, in J K–1 mol–1, for the reaction between nitrogen and hydrogen to form ammonia?

N2 + 3H2 → 2NH3

   Standard molar entropy / J K–1 mol–1
H2 130.6
N2 191.6
NH3 192.3

  • –198.8

  • –129.9

  • +129.9

  • +198.8

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3
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The entropy change of the surroundings, ΔSsurroundings, and the entropy change of the system,  ΔSsystem, for four different reactions are given.

Reaction ΔSsurroundings / J K−1 mol−1 ΔSsystem / J K−1 mol−1
P +245 +34
Q +350 −276
R −482 +65
S −563 −128

Which of these is thermodynamically feasible?

  • reaction P only

  • reactions P and Q only

  • reaction R only

  • reactions R and S only

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41 mark

Ammonium nitrate is very soluble in water.

NH4NO3 (s) + aq → Nstraight H subscript 4 superscript plus (aq) + Nstraight O subscript 3 superscript minus (aq)  ∆H to the power of ⦵= +25.8 kJ mol−1

What is the best explanation for this?

  • all ammonium salts are soluble in water

  • the activation energy of the reaction is very low

  • the enthalpies of hydration of the ions are very exothermic

  • the entropy change of the system, ∆Ssystem , is positive

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51 mark

The decomposition of calcium carbonate is an important reaction in the manufacture of cement.

CaCO3 (s) → CaO (s) + CO2 (g)     ∆H to the power of ⦵= +178 kJ mol−1

What are the signs of the entropy change of the system, ∆Ssystem , and of the entropy change of the surroundings, ∆Ssurroundings ?

      Sign of ∆Ssystem Sign of ∆Ssurroundings
  ☐ A positive positive
  ☐ B positive negative
  ☐ C negative positive
  ☐ D negative negative

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    61 mark

    The standard molar entropy, S to the power of ⦵, of a substance

    • is not affected by changes of state or changes in temperature

    • only changes when the temperature changes

    • only changes when the substance changes state

    • changes when the temperature changes and when the substance changes state

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    71 mark

    The standard enthalpy change of solution of potassium chloride, KCl, is +17 kJ mol−1.

    The solubility of potassium chloride in water at 298 K is 359 g dm−3.

    Which of these explains the solubility of potassium chloride in water?

    • the hydration enthalpy of K+ and the lattice energy of KCl are exothermic

    • the hydration enthalpy of K+ and the lattice energy of KCl are endothermic

    • the total entropy change when KCl dissolves is positive

    • the total entropy change when KCl dissolves is negative

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