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CAIE A-Level Chemistry 23.3.3 Standard Entropy Change Calculations

Practise calculating standard reaction entropy from tabulated molar entropies with stoichiometric multipliers.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • multiply every standard molar entropy by its balanced-equation coefficient
  • calculate ΔS° as the sum for products minus the sum for reactants, preserving every sign
  • report the result in J K−1 mol−1 and use its sign to check the expected particle change

23.3.3—The entropy change for a reaction, ΔS question 1

[Maximum number: 1]

Potassium iodide, KI, is used as a reagent in both inorganic and organic chemistry.

KI slowly oxidises in air, forming I2\mathrm{I}_{2}.

reaction \(1 \quad 4 \mathrm{KI}(\mathrm{s})+2 \mathrm{CO}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{~K}_{2} \mathrm{CO}_{3}(\mathrm{~s})+2 \mathrm{I}_{2}(\mathrm{~s}) \quad \Delta H^{\ominus}=-203.4 \mathrm{~kJ} \mathrm{~mol}^{-1}\)

Table 1.2 shows some data relevant to this question.

Table 1.2

Table 1.2

Calculate the standard entropy change, ΔS⊖\Delta S^{\ominus}, of reaction 1 .

ΔS⊖=…………………………………..JK−1 mol−1\Delta S^{\ominus}=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . . \mathrm{JK}^{-1} \mathrm{~mol}^{-1}
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