OnlineCBT
Chemistry · THERMODYNAMICS
हिन्दीFor the dissociation of crystal lattice: \( \text{NaCl}(s) \rightarrow \text{Na}^+(g) + \text{Cl}^-(g) \), the lattice enthalpy is \( \Delta_{\text{lattice}} H^\ominus = +788\text{ kJ mol}^{-1} \) at \( 298\text{ K} \). Assuming ideal gas behavior for ions, what is the change in internal energy (\( \Delta_{\text{lattice}} U^\ominus \))? (Take \( 2RT \approx 5\text{ kJ mol}^{-1} \))
Correct answer · Option 4
\( +783\text{ kJ mol}^{-1} \)
Explanation
\( \Delta H = \Delta U + \Delta n_g RT \). Here \( \Delta n_g = 2 - 0 = 2 \), so \( \Delta U = \Delta H - 2RT = 788 - 5 = +783\text{ kJ mol}^{-1} \).
