Thermodynamics and Thermochemistry 2 Question 31
31. The standard heats of formation of $\mathrm{CCl}{4}(g), \mathrm{H}{2} \mathrm{O}(g)$, $\mathrm{CO}_{2}(g)$ and $\mathrm{HCl}(g)$ at $298 \mathrm{~K}$ are $-25.5,-57.8,-94.1$ and $-22.1 \mathrm{kcal} / \mathrm{mol}$ respectively. Calculate $\Delta H^{\circ}(298 \mathrm{~K})$ for the reaction
$\mathrm{CCl}{4}(g)+2 \mathrm{H}{2} \mathrm{O}(g) \longrightarrow \mathrm{CO}_{2}(g)+4 \mathrm{HCl}(g)(1982,2 \mathrm{M})$
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Solution:
- $\Delta H_{r}^{\circ}=\Sigma \Delta_{f} H^{\circ}$ (products) $-\Sigma \Delta_{f} H^{\circ}$ (reactants)
$$ =-94.1+4(-22.1)-(-25.5-2 \times 57.8) $$
$$ =-41.4 \mathrm{kcal} $$
