Chemistry - Chemical Equilibrium Question with Solution | TestHub

Key Idea: $\Delta H_{\text{reaction }}=\Sigma$ Bond energy of reactant $-\Sigma$ Bond energy of product $\begin{array}{ll}\text{Here, }& \Delta {\mathrm{H}}_{\mathrm{H}-\mathrm{H}}=434\mathrm{kJ}{\mathrm{mol}}^{-1}\\ & \Delta {\mathrm{H}}_{\mathrm{Cl}-\mathrm{Cl}}=242\mathrm{kJ}{\mathrm{mol}}^{-1}\\ & \Delta {\mathrm{H}}_{\mathrm{H}-\mathrm{Cl}}=431\mathrm{kJ}{\mathrm{mol}}^{-1}\\ \because & \frac{1}{2}{\mathrm{H}}_2+\frac{1}{2}{\mathrm{Cl}}_2⟶\mathrm{HCl}\end{array}$ $\begin{array}{rl}\Delta H_{\text{reaction }}& =\frac{1}{2}\Delta H_{\mathrm{H}-\mathrm{H}}+\frac{1}{2}\Delta {\mathrm{H}}_{\mathrm{Cl}-\mathrm{Cl}}-\Delta {\mathrm{H}}_{\mathrm{H}-\mathrm{Cl}}\\ & =\frac{1}{2}\times 434+\frac{1}{2}\times 242-431\\ & =217+121-431\\ & =-93\mathrm{kJ}{\mathrm{mol}}^{-1}\end{array}$