Thermodynamics and Thermochemistry 2 Question 11
11. Which of the following reactions defines $\Delta H_{f}^{\circ}$ ?
(a) $\mathrm{C}{\text {(diamond) }}+\mathrm{O}{2}(g) \longrightarrow \mathrm{CO}_{2}(g)$
(2003, 1M)
(b) $\frac{1}{2} \mathrm{H}{2}(g)+\frac{1}{2} \mathrm{~F}{2}(g) \longrightarrow \mathrm{HF}(g)$
(c) $\mathrm{N}{2}(g)+3 \mathrm{H}{2}(g) \longrightarrow 2 \mathrm{NH}_{3}(g)$
(d) $\mathrm{CO}(g)+\frac{1}{2} \mathrm{O}{2}(g) \longrightarrow \mathrm{CO}{2}(g)$
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Solution:
- $\frac{1}{2} \mathrm{H}{2}(g)+\frac{1}{2} \mathrm{~F}{2}(g) \longrightarrow \mathrm{HF}(g)$
Here $\Delta H^{\circ}=$ Standard molar enthalpy of formation of $\mathrm{HF}(g)$.
