For $\mathrm{NaCl}_{(\mathrm{s})}$ enthalpy of solution is $4 \mathrm{~kJ} \mathrm{~mol}^{-1}$ and lattice…

For $\mathrm{NaCl}_{(\mathrm{s})}$ enthalpy of solution is $4 \mathrm{~kJ} \mathrm{~mol}^{-1}$ and lattice enthalpy is $790 \mathrm{~kJ} \mathrm{~mol}^{-1}$. What is hydration enthalpy of $\mathrm{NaCl}$ ?
  1. $786 \mathrm{~kJ}$
  2. $794 \mathrm{~kJ}$
  3. $-786 \mathrm{~kJ}$
  4. $-794 \mathrm{~kJ}$

Solution

$\begin{aligned} \Delta_{\text {soln }} \mathrm{H} & =\Delta_{\mathrm{L}} \mathrm{H}+\Delta_{\text {hyd }} \mathrm{H} \\ \therefore \quad \Delta_{\text {hyd }} \mathrm{H} & =\Delta_{\text {soln }} \mathrm{H}-\Delta_{\mathrm{L}} \mathrm{H} \\ & =4 \mathrm{~kJ} \mathrm{~mol}^{-1}-790 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ & =-786 \mathrm{~kJ} \mathrm{~mol}^{-1}\end{aligned}$

Asked in: MHT CET 2023 (09 May Shift 2)

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