Search any question & find its solution
Question:
Answered & Verified by Expert
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) $\mathrm{H}_2(g)+1 / 2 \mathrm{O}_2(g) \rightarrow \mathrm{H}_2 \mathrm{O}(l) \Delta H=-286.2$ $\mathrm{kJ}$
Options:
(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) $\mathrm{H}_2(g)+1 / 2 \mathrm{O}_2(g) \rightarrow \mathrm{H}_2 \mathrm{O}(l) \Delta H=-286.2$ $\mathrm{kJ}$
Solution:
2005 Upvotes
Verified Answer
The correct answer is:
$-891.9$
$$
\mathrm{CH}_4(g)+2 \mathrm{O}_2(g) \longrightarrow \mathrm{CO}_2(g)+2 \mathrm{H}_2 \mathrm{O}
$$
(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 $\Delta H$
$$
\begin{gathered}
\therefore \Delta H=+74.8+(-393.5)+(-286.2 \times 2) \\
=-891.1 \mathrm{~kJ}
\end{gathered}
$$
\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}
$$
Looking for more such questions to practice?
Download the MARKS App - The ultimate prep app for IIT JEE & NEET with chapter-wise PYQs, revision notes, formula sheets, custom tests & much more.