The standard enthalpies of formation of , , , and are -110, -393, +81, and +9.7 kJ/mol respectively. — Thermodynamics and Thermochemistry Chemistry Question
Question
The standard enthalpies of formation of $CO(g)$, $CO_2(g)$, $N_2O(g)$, and $N_2O_4(g)$ are -110, -393, +81, and +9.7 kJ/mol respectively. Calculate the enthalpy change ($\Delta H$) for the reaction: $N_2O_4(g) + 3CO(g) \rightarrow N_2O(g) + 3CO_2(g)$.
Answer: A
💡 Solution & Explanation
By Hess's law, $\Delta H = \sum \Delta H_f^\circ(products) - \sum \Delta H_f^\circ(reactants) = [81 + 3(-393)] - [9.7 + 3(-110)] = - [9.7 - 330] = -1098 - (-320.3) = -777.7$ kJ/mol.
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