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AP®ChemistryCollege BoardExam QuestionsUnit 9: Thermodynamics & ElectrochemistryEntropy

Entropy (College Board AP® Chemistry)

Exam Questions

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Entropy

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Entropy

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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

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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31 mark

Condensation appears on a bathroom mirror. Which of the following is true?

  • The condensation is the result of a positive enthalpy change and negative entropy change

  • The condensation is the result of a negative enthalpy change and positive entropy change

  • The condensation is the result of a positive enthalpy change and positive entropy change

  • The condensation is the result of a negative enthalpy change and negative entropy change

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41 mark

Which reaction occurs with the largest increase in entropy?

  • Pb(NO3)2 (s) + 2KI (s) → PbI2 (s) + 2KNO3 (s) 

  • CaCO3 (s) →  CaO (s) + CO2 (g)

  • 3H2 (g) + N2 (g) →  2NH3 (g)

  • H2 (g) + I2 (g) → 2HI(g)

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11 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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21 mark

W + X → 2Y + Z

The entropies of formation the four substances shown in the reaction are:

SW = -10 J/mol

SX= +15 J/mol

SY = -75 J/mol

SZ =-45 J/mol

For the reaction shown, determine the correct entropy change.

  • -115 J/mol

  • -125 J/mol

  • -200 J/mol

  • 200 J/mol

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31 mark

CaCO3 (s) rightwards harpoon over leftwards harpoon CaO (s) + CO2 (g)

Which factors will increase the entropy of this system?

I.     Increasing the temperature without changing the volume of the container.

II.     Decreasing the concentration of the gas without changing the volume of the container.

III.     Increasing the pressure without changing the volume of the container.

  • I and II only

  • I and III only

  • II and III only

  • I, II and III

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