Question

In an oven, using $10 kg$ coal (assume the coal is $80 \%$ carbon in weight), insufficient oxygen is supplied such that $60 \%$ of carbon is converted to $CO _{2}$ and $40 \%$ carbon is converted to $CO$. The heat generated, when coal is burnt in this fashion would be
Given : $C _{(s)}+ O _{2(g)} \rightarrow CO _{2( g )} ;\,\,\,\, \Delta H=-394 kJ$
$C _{(s)}+\frac{1}{2} O _{2(g)} \rightarrow CO _{(g)}; \,\,\,\, \Delta H=-111\, kJ$

• A. $183200\, kJ$
• B. $187200\, kJ$
• C. $185200\, kJ$
• D. $181200\, kJ$

Answer 1

Answer: (B)

As coal has $80 \%$ carbon in weight

weight of carbon in $10\, kg$ coal $=10 \times \frac{80}{100}=8 \, kg =8000 \, g$

As $60 \%$ of $C$ is converted to $CO _{2}$ thus wt. of $C$ converted into

$CO _{2}=8000 \times \frac{60}{100}=4800 \, g$

and $40 \%$ of $C$ to $C O$ thus $w t$. of $C$ converted into $C O$

$=8000 \times \frac{40}{100}=3200 \, g$

$12 g (1 mole )$ of $C$ on combustion liberates $=394 \, kJ$ of heat

$\therefore \,\,\,\ 4800 g$ of $C$ on combustion liberates

$=\frac{394 \times 4800}{12} kJ =157600 \, kJ \ldots ..(i)$

$12 g (1 mole )$ of $C$ on combusion liberates $=111 \, kJ$ of heat

$\therefore 3200 \, g$ of $C$ on combustion liberates

$=\frac{111 \times 3200}{12} kJ$

$=29600 \, kJ$

Total heat liberated would be

$=157600+29600=187200 \, kJ$