The molar heat capacities of A, B and C are in the ratio 1:2:3. The enthalpy change for the reaction — Thermodynamics and Thermochemistry Chemistry Question
Question
The molar heat capacities of A, B and C are in the ratio 1:2:3. The enthalpy change for the reaction $\text{A} + \text{B} \to \text{C}$ at temperature $T_1$ is $\Delta H_1$. Assuming that the heat capacities do not change with temperature, the enthalpy change, $\Delta H_2$, at temperature, $T_2$ ($T_2 > T_1$) will be
Answer: B
💡 Solution & Explanation
According to Kirchhoff's law, $\Delta H_2 - \Delta H_1 = \Delta C_P(T_2 - T_1)$. Here, $\Delta C_P = C_P(\text{C}) - [C_P(\text{A}) + C_P(\text{B})]$. Given the ratio 1:2:3, $\Delta C_P = 3x - (1x + 2x) = 0$. Since $\Delta C_P = 0$, the enthalpy change is constant ($\Delta H_2 = \Delta H_1$).
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