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CAIE A-Level Chemistry 23.2.3 Enthalpy of Solution Calculations

Practise calculating solution, hydration or lattice terms from energy cycles with coefficients and correct signs.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • multiply each ionic hydration enthalpy by its coefficient in the ionic formula
  • subtract formation lattice energy when calculating ΔHsol from summed hydration values
  • retain negative data signs explicitly before evaluating and report the final kJ mol−1 sign

23.2.3—Calculations: the energy cycles in 23.2.2 question 1

[Maximum number: 2]

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

Table 1.1 gives some data about the halide ions, Cl−,Br−\mathrm{Cl}^{-}, \mathrm{Br}^{-}and I−\mathrm{I}^{-}, and their potassium salts.

Table 1.1

Table 1.1

The enthalpy change of solution of KI(s) is +21.0 kJ mol−1+21.0 \mathrm{~kJ} \mathrm{~mol}^{-1}.

Use this information and the data in Table 1.1 to calculate the enthalpy change of hydration of the potassium ion, K+(g)\mathrm{K}^{+}(\mathrm{g}).

ΔHhyd  of K+(g)=……………………………………..kJ mol−1\Delta H_{\text {hyd }} \text { of } \mathrm{K}^{+}(\mathrm{g})=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . . \mathrm{kJ} \mathrm{~mol}^{-1}
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