Calculate the enthalpy of formation of from the following data:<br>(i) <br>(ii) <br>(iii) <br>(iv) < — Thermodynamics and Thermochemistry Chemistry Question
Question
Calculate the enthalpy of formation of $\text{I}_2\text{O}_5\text{(s)}$ from the following data:<br>(i) $\text{I}_2\text{O}_5\text{(s)} + \text{H}_2\text{O(l)} \to 2\text{HIO}_3\text{(aq)}; \Delta H = +4.0\text{ kJ}$<br>(ii) $\text{KI(aq)} + 3\text{HClO(aq)} \to \text{HIO}_3\text{(aq)} + 2\text{HCl(aq)} + \text{KCl(aq)}; \Delta H = -322.0\text{ kJ}$<br>(iii) $\text{NaOH(aq)} + \text{HClO(aq)} \to \text{NaOCl(aq)} + \text{H}_2\text{O(l)}; \Delta H = -44.0\text{ kJ}$<br>(iv) $\text{NaOH(aq)} + \text{HCl(aq)} \to \text{NaCl(aq)} + \text{H}_2\text{O(l)}; \Delta H = -57.0\text{ kJ}$<br>(v) $2\text{NaOH(aq)} + \text{Cl}_2\text{(g)} \to \text{NaOCl(aq)} + \text{NaCl(aq)} + \text{H}_2\text{O(l)}; \Delta H = -100.0\text{ kJ}$<br>(vi) $2\text{KI(aq)} + \text{Cl}_2\text{(g)} \to 2\text{KCl(aq)} + \text{I}_2\text{(s)}; \Delta H = -224.0\text{ kJ}$<br>(vii) $\text{H}_2\text{(g)} + 1/2 \text{O}_2\text{(g)} \to \text{H}_2\text{O(l)}; \Delta H = -285.0\text{ kJ}$<br>(viii) $1/2 \text{H}_2\text{(g)} + 1/2 \text{Cl}_2\text{(g)} \to \text{HCl(g)}; \Delta H = -92.0\text{ kJ}$<br>(ix) $\text{HCl(g)} + \text{aq} \to \text{HCl(aq)}; \Delta H = -75.0\text{ kJ}$
💡 Solution & Explanation
Using Hess's law to form $\text{I}_2\text{(s)} + 5/2\text{O}_2\text{(g)} \to \text{I}_2\text{O}_5\text{(s)}$, systematically combine the 9 equations to eliminate all intermediates ($\text{HIO}_3$, KI, HClO, $\text{H}_2\text{O}$, NaOH, NaOCl, etc.). The net linear combination evaluates exactly to $-173.0\text{ kJ}$.