The following are various values (kJ per mol): ; ; ; ; . The Lattice enthalpy of is — Thermodynamics and Thermochemistry Chemistry Question
Question
The following are various $\Delta H$ values (kJ per mol): $\Delta_f H\text{ (NaCl)} = -411.2$; $\Delta_f H\text{ (Na, g)} = 107.3$; $\Delta_f H\text{ (Cl, g)} = 121.7$; $\Delta_i H\text{ (Na, g)} = 495.4$; $\Delta_{\text{eg}} H\text{ (Cl, g)} = 348.5$. The Lattice enthalpy of $\text{NaCl(s)}$ is
Answer: D
💡 Solution & Explanation
Born-Haber cycle equates: $\Delta_f H(\text{NaCl}) = \Delta_f H(\text{Na, g}) + \Delta_i H(\text{Na}) + \Delta_f H(\text{Cl, g}) - \Delta_{\text{eg}} H(\text{Cl}) - \text{LE}$. $-411.2 = 107.3 + 495.4 + 121.7 - 348.5 - \text{LE} \implies -411.2 = 375.9 - \text{LE} \implies \text{LE} = 787.1\text{ kJ/mol}$.
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