A natural gas may be assumed to be a mixture fo methane and ethane only. On complete combustion of `10L` of gas at `STP` the heat evolved was `474.6 kJ`. Assuming `Delta_(comb) H^(Theta) CH_(4)(g) =- 894 kJ mol^(-1)` and composition of the mixture by volume.

Explanation

`xL rarr CH_(4), "mole of" CH_(4) = x //22.4`
`(10-x) L rarr C_(2)H_(6), "mole of" C_(2)H_(6) = (10-x)//22.4`
Heat evolved `= (x)/(22.4) xx 894 +((10-x))/(22.4) xx 1500`
`474.6 = (x)/(22.4) xx 894 +((10-x))/(22.4) xx 1500`
`x = 0.745, % CH_(4) = 74.5%`