Given two processes:<br>(i) <br>(ii) <br>The value of of is — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

The standard enthalpy of formation involves forming 1 mole of product. Multiply eq (i) by 0.5: $1/4 \text{P}_4 + 1.5 \text{Cl}_2 \to \text{PCl}_3$ ($\Delta H = -317.5$). Add eq (ii): $\text{PCl}_3 + \text{Cl}_2 \to \text{PCl}_5$ ($\Delta H = -137$). Total $\Delta H = -317.5 - 137 = -454.5\text{ kJ/mol}$.