The lattice energy of is 205 kJ/mol and the hydration energies of and ions are –80 and –40 kJ/mol, r — Thermodynamics and Thermochemistry Chemistry Question
Question
The lattice energy of $\text{Na}_2\text{CO}_3\text{(s)}$ is 205 kJ/mol and the hydration energies of $\text{Na}^+$ and $\text{CO}_3^{2-}$ ions are –80 and –40 kJ/mol, respectively. The correct prediction about the solubility of $\text{Na}_2\text{CO}_3$ in water is (Assume that $\Delta H$ is independent of temperature.)
Answer: A
💡 Solution & Explanation
Calculate $\Delta H_{\text{sol}} = \text{LE} + \Sigma \Delta H_{\text{hyd}} = 205 + [2(-80) + (-40)] = 205 - 200 = +5\text{ kJ/mol}$. Because the dissolution process is endothermic, increasing the temperature provides necessary heat, thus increasing solubility.
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