Thermodynamics And Thermochemistry Result Question 4
4. The heats of combustion of carbon and carbon monoxide are $-393.5$ and $-283.5 \mathrm{~kJ} \mathrm{~mol}^{-1}$, respectively. The heat of formation (in kJ ) of carbon monoxide per mole is
(2016 Main)
(a) $676.5$
(b) $-676.5$
(c) $-110.5$
(d) $110.5$
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Answer:
Correct Answer: 4. (c)
Solution:
- $\mathrm{C}(s)+\mathrm{O}_2(g) \longrightarrow \mathrm{CO}_2(g) ; \Delta H=-393.5 \mathrm{~kJ} \mathrm{~mol}^{-1}$ ……(i)
$\mathrm{CO}+\frac{1}{2} \mathrm{O}_2 \longrightarrow \mathrm{CO}_2(\mathrm{~g}) ; \Delta H=-283.5 \mathrm{~kJ} \mathrm{~mol}^{-1}$ ……(ii)
On subtracting Eq. (ii) from Eq. (i), we get
$\begin{aligned} & \mathrm{C}(s)+\frac{1}{2} \mathrm{O}_2(\mathrm{~g}) \longrightarrow \mathrm{CO}(\mathrm{g}) \text {; } \\ & \Delta H=(-393.5+283.5) \mathrm{kJ} \mathrm{mol}^{-1} \\ & =-110 \mathrm{~kJ} \mathrm{~mol}^{-1} \text { (approx.) } \\ & \end{aligned}$
BETA
