The intermediate is formed in the thermal decomposition of silicon hydrides. Calculate of from the f — Thermodynamics and Thermochemistry Chemistry Question
Question
The intermediate $\text{SiH}_2$ is formed in the thermal decomposition of silicon hydrides. Calculate $\Delta H^\circ_f$ of $\text{SiH}_2$ from the following reactions:<br>$\text{Si}_2\text{H}_6\text{(g)} + \text{H}_2\text{(g)} \to 2\text{SiH}_4\text{(g)}; \Delta H^\circ = -11.7\text{ kJ/mol}$<br>$\text{SiH}_4\text{(g)} \to \text{SiH}_2\text{(g)} + \text{H}_2\text{(g)}; \Delta H^\circ = +239.7\text{ kJ/mol}$<br>$\Delta H^\circ_f, \text{Si}_2\text{H}_6\text{(g)} = +80.3\text{ kJ mol}^{-1}$
💡 Solution & Explanation
From Eq 1: $-11.7 = 2\Delta H_f(\text{SiH}_4) - 80.3 \implies 2\Delta H_f(\text{SiH}_4) = 68.6 \implies \Delta H_f(\text{SiH}_4) = 34.3\text{ kJ/mol}$. From Eq 2: $239.7 = \Delta H_f(\text{SiH}_2) - 34.3 \implies \Delta H_f(\text{SiH}_2) = 239.7 + 34.3 = 274.0\text{ kJ/mol}$.