CAIE A-Level Chemistry 23.2.2 Solution, Lattice and Hydration Cycle

Practise constructing energy cycles that connect an ionic solid, gaseous ions and hydrated aqueous ions.

Exam points

place the solid, separated gaseous ions and aqueous ions at the three cycle states
sum cation and anion hydration terms with formula multipliers for the gaseous-to-aqueous route
apply the formation-lattice convention so the cycle gives ΔHsol = ΣΔHhyd − ΔHlatt

[Maximum number: 1]

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

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

Table 1.1

The $\Delta H_{\text {sol }}$ values of these potassium halides are almost constant.

Use the $\Delta H_{\text {hyd }}$ and $\Delta H_{\text {latt }}$ data in Table 1.1 to suggest why.

the difference between $\Delta H_{\text {latt }}$ and $\Delta H_{\text {hyd }}$ remains roughly constant

OR $\Delta H_{\text {latt }}$ and $\Delta H_{\text {hyd }}$ become less exothermic by a similar amount

All question bank results loaded

23.2.2—An energy cycle involving enthalpy change question 1