Thermodynamics and Thermochemistry 2 Question 4
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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 $\mathrm{kJ}$ ) of carbon monoxide per mole is
======= ####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 $\mathrm{kJ}$ ) of carbon monoxide per mole is
3e0f7ab6f6a50373c3f2dbda6ca2533482a77bed (a) 676.5
(b) -676.5
(c) -110.5
(d) 110.5
(2016 Main)
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Solution:
- $\mathrm{C}(s)+\mathrm{O}{2}(g) \longrightarrow \mathrm{CO}{2}(g) ; \Delta H=-393.5 \mathrm{~kJ} \mathrm{~mol}^{-1}$
$\mathrm{CO}+\frac{1}{2} \mathrm{O}{2} \longrightarrow \mathrm{CO}{2}(g) ; \Delta H=-283.5 \mathrm{~kJ} \mathrm{~mol}^{-1}$
On subtracting Eq. (ii) from Eq. (i), we get
$$ \begin{aligned} \mathrm{C}(s)+\frac{1}{2} \mathrm{O}_{2}(g) & \longrightarrow \mathrm{CO}(g) ; \ \Delta H & =(-393.5+283.5) \mathrm{kJ} \mathrm{mol}^{-1} \ & =-110 \mathrm{~kJ} \mathrm{~mol}^{-1} \text { (approx.) } \end{aligned} $$
