Q44 / 200 · TS EAMCET 2002 · Chemistry
Calculate the heat of combustion (in $\mathrm{kJ}$ ) of methane from the following data:
(i)
$$
\mathrm{C}_{\text {(graphite) }}+2 \mathrm{H}_2(g) \rightarrow \mathrm{CH}_4(g) \quad \Delta H=-74.8
$$
(ii)
$$
\mathrm{C}_{\text {(graphite) }}+\mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g) \quad \Delta H=-393.5
$$
(iii) $\mathrm{H}_2(g)+1 / 2 \mathrm{O}_2(g) \rightarrow \mathrm{H}_2 \mathrm{O}(l) \Delta H=-286.2$ $\mathrm{kJ}$
- Correct answerA$-891.9$
- B$-816.3$
- C$-965.9$
- D$-1040.7$
Solution
$$
\mathrm{CH}_4(g)+2 \mathrm{O}_2(g) \longrightarrow \mathrm{CO}_2(g)+2 \mathrm{H}_2 \mathrm{O}
$$
(l) $\Delta H=$ ?
To get this equation reverse equation (i) write equation (ii) as it is, multiply equation (iii) by 2 and add all these equations, we will get $\Delta H$
$$
\begin{gathered}
\therefore \Delta H=+74.8+(-393.5)+(-286.2 \times 2) \\
=-891.1 \mathrm{~kJ}
\end{gathered}
$$
Hence, the correct answer is option: 'A'.