AP®ChemistryCollege BoardExam QuestionsUnit 9: Thermodynamics & ElectrochemistryEntropy

Entropy (College Board AP® Chemistry)

Exam Questions

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Entropy

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Entropy

11 mark

Which species are arranged in order of increasing entropy?

  • C2H6 (g)  >  C2H5OH (l)  > Hg (l)  >  Mg (s)

  • C2H5OH (l)  >  C2H6 (g)  >  Hg (l)  >  Mg (s)

  • Mg (s)  >  C2H5OH (l)  >  Hg (l)  >  C2H6 (g)

  • Mg (s)  >  Hg (l)  >  C2H5OH (l)  >  C2H6 (g) 

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21 mark

4HCl (g) + O2 (g) rightwards harpoon over leftwards harpoon 2Cl2 (g) + 2H2O (g)

Hydrogen chloride undergoes a reversible reaction to form chlorine as shown above.

 

HCl (g)

O2 (g)

Cl2 (g)

H2O (g)

S/ J K–1 mol–1

187

205

223

189

Using the information above, calculate the standard entropy change, ΔS, for this reaction. 

  • –129 J K–1 mol–1

  • +129 J K–1 mol–1

  • -20 J K–1 mol–1

  • +20 J K–1 mol–1

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31 mark

Which of the following reactions would show an increase in entropy?

(Assume all reactants and products are in their standard state).

I. The reaction between zinc and nitric acid

II. The thermal decomposition of calcium carbonate

III. The complete combustion of methane

  • I only

  • I and II only

  • I and III only

  • I, II and III

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