$28.0\mathrm{L}\text{ of }{\mathrm{CO}}_2$ is produced on complete combustion of 16.8 L gaseous mixture of ethane and methane at 25⁰C and 1 atm. Heat evolved during the combustion process is ___________ kJ.
Given ${\mathrm{\Delta H}}_{\mathrm{c}}\left({\mathrm{CH}}_4\right)=-900\mathrm{kJ}{\mathrm{mol}}^{-1};{\mathrm{\Delta H}}_{\mathrm{C}}\left({\mathrm{C}}_2{\mathrm{H}}_4\right)=-1400\mathrm{kJ}{\mathrm{mol}}^{-1}$

Ethen + methane mixture
$\begin{array}{c}{\mathrm{C}}_2{\mathrm{H}}_4+3{\mathrm{O}}_2\to \underset{\mathrm{aL}}{2{\mathrm{CO}}_2+2{\mathrm{H}}_2\mathrm{O}}\\ 2\mathrm{a}\\ {\mathrm{CH}}_4+2{\mathrm{O}}_2\to {\mathrm{CO}}_2+2{\mathrm{H}}_2\mathrm{O}\end{array}$
Total volume of ${\mathrm{CO}}_2=(16.8-\mathrm{a}+2\mathrm{a})\mathrm{L}=16.8+\mathrm{aL}=28.026$
$\begin{array}{l}\mathrm{a}=28.02-16.8=11.226\\ {\mathrm{V}}_{{\mathrm{C}}_2{\mathrm{H}}_4}=11.22\mathrm{L}{\mathrm{V}}_{{\mathrm{CH}}_4}=5.58\mathrm{L}\\ { }^{{\mathrm{n}}^2}{\mathrm{C}}_2{\mathrm{H}}_4=0.5008{\mathrm{n}}_{{\mathrm{CH}}_4}=0.249\text{ mole }\\ {\mathrm{\Delta }}_0\mathrm{H}{\mathrm{CH}}_4\Rightarrow 1\text{ mole }{\mathrm{CH}}_4\text{ gives }900\mathrm{KT}\\ {\mathrm{\Delta }}_0{\mathrm{HC}}_2{\mathrm{H}}_2\Rightarrow 1\mathrm{mole}\text{ of }{\mathrm{C}}_2{\mathrm{H}}_4\text{ give }=1400\mathrm{kJ}\\ \end{array}$
total energy og combustion
$\begin{array}{r}=0.5008\times 1400+0.249\times 900\\ =701.12+224.1=925.22\mathrm{KJ}\end{array}$