Calculate the heat of reaction at 77 C for if the heat of reaction at 27 C is -22.1 kcal. The molar — Thermodynamics and Thermochemistry Chemistry Question
Question
Calculate the heat of reaction at 77 C for $0.5H_2(g) + 0.5Cl_2(g) \rightarrow HCl(g)$ if the heat of reaction at 27 C is -22.1 kcal. The molar heat capacities ($C_p$) at 27 C for $H_2$, $Cl_2$, and $HCl$ are 6.82, 7.70, and 6.80 cal/K-mol respectively.
Answer: A
💡 Solution & Explanation
According to Kirchhoff's equation, $\Delta H_{T_2} = \Delta H_{T_1} + \Delta C_p(T_2 - T_1)$. $\Delta C_p = 6.80 - [0.5(6.82) + 0.5(7.70)] = -0.46 \text{ cal/K}$. $\Delta T = 50 \text{ K}$. $\Delta H_{350} = -22.1 \text{ kcal} + \frac{-0.46 \times 50}{1000} \text{ kcal} = -22.123 \text{ kcal}$.
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