Question

What will be the amount of heat evolved by burning 10 L of methane under standard conditions?
(Given heat of formation $C{H}_4,C{O}_2$ and $H_{2}O$ are $-76.2,-398.8$ and $-241kJmo{l}^{-1}$ respectively)

• A. 805.8 kJ
• B. 398.8 kJ
• C. 359.2 kJ
• D. 640.4 kJ

Answer 1

Answer: (C)

359.2 kJ

$C{H}_4+2O_2\to C{O}_2+2H_{2}O$

$\Delta H_{comb}=\Delta H_{f\left(C{O}_2\right)}+2\times \Delta H_{f\left(H_{2}O\right)}-\Delta H_{f\left(C{H}_4\right)}$

$\Delta H_{comb}=-398.8-2\times (-241)-(-76.2)=-804.6kJ/mol$

1 mol at STP $=22.4L$

For combustion of 10 L of methane

$\Delta H_{comb}=\frac{-804.6}{22.4}\times 10=359.2kJ$