OnlineCBT
Chemistry · THERMODYNAMICS
हिन्दीConsider the following thermochemical reactions: (i) \( \text{C}(\text{graphite}) + \text{O}_2(g) \rightarrow \text{CO}_2(g) \); \( \Delta_r H^\ominus = -393.5\text{ kJ mol}^{-1} \) (ii) \( \text{CO}(g) + \frac{1}{2}\text{O}_2(g) \rightarrow \text{CO}_2(g) \); \( \Delta_r H^\ominus = -283.0\text{ kJ mol}^{-1} \) Applying Hess's law, the standard enthalpy of formation of \( \text{CO}(g) \) is:
Correct answer · Option 2
-110.5 kJ mol⁻¹
Explanation
Target reaction: \( \text{C}(\text{graphite}) + \frac{1}{2}\text{O}_2(g) \rightarrow \text{CO}(g) \). Subtracting reaction (ii) from (i): \( \Delta_f H^\ominus[\text{CO}(g)] = -393.5 - (-283.0) = -110.5\text{ kJ mol}^{-1} \).
