The hydration energies of $\mathrm{K}^{+}$ and $\mathrm{Cl}^{-}$ are -x and -y $\mathrm{kJ} / \mathrm{mol}$ respectively. If lattice energy of KCl is -z $\mathrm{kJ} / \mathrm{mol}$, then the heat of solution of KCl is :

JEE Main · 2025 · 07 Apr 2025 · Shift 2 · Chemical Thermodynamics

The hydration energies of

K^{+}

and

Cl^{-}

are -x and -y

kJ / mol

respectively. If lattice energy of KCl is -z

kJ / mol

, then the heat of solution of KCl is :

(A) $+ x - y - z$
(B) $x + y + z$
(C) $z - (x + y)$ ✓ Correct
(D) $- z - (x + y)$

Answer: (C)

Solution

Dissolving the solid first requires the lattice to be pulled apart and then releases energy as the gaseous ions are hydrated. The lattice energy is given as

- z

, so breaking the lattice costs

+ z

, while hydration of the two ions releases

- x

and

- y

. Adding these contributions, the heat of solution is

z + (- x) + (- y) = z - (x + y)

JEE Main · 2025 · 07 Apr 2025 · Shift 2 · Single correct option

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