Lattice enthalpy and enthalpy of solution of NaCl are $788 \mathrm{~kJ} \mathrm{~mol}^{-1}$ and $4 \mathrm{~kJ} \mathrm{~mol}^{-1}$, respectively. The hydration enthalpy of NaCl is:

(B) $-784 \mathrm{~kJ} \mathrm{~mol}^{-1}$

(A) $784 \mathrm{~kJ} \mathrm{~mol}^{-1}$

(C) $780 \mathrm{~kJ} \mathrm{~mol}^{-1}$

(D) $-780 \mathrm{~kJ} \mathrm{~mol}^{-1}$

JEE Main · 2020 · 05 Sep 2020 · Shift 2 · Chemical Thermodynamics

Lattice enthalpy and enthalpy of solution of NaCl are

788 kJ mol^{- 1}

and

4 kJ mol^{- 1}

, respectively. The hydration enthalpy of NaCl is:

Answer: (B)

By Hess's law the enthalpy of solution is the sum of the lattice enthalpy and the hydration enthalpy,

Δ H_{so l} = Δ H_{l a tt i ce} + Δ H_{h y d}

. Here

4 = 788 + Δ H_{h y d}

, so

Δ H_{h y d} = 4 - 788 = - 784

kJ mol

^{- 1}

, the negative value marking hydration as exothermic.

JEE Main · 2020 · 05 Sep 2020 · Shift 2 · Single correct option