JEE MAIN - Chemistry (2024 - 4th April Morning Shift - No. 24)
The enthalpy of formation of ethane $$(\mathrm{C}_2 \mathrm{H}_6)$$ from ethylene by addition of hydrogen where the bond-energies of $$\mathrm{C}-\mathrm{H}, \mathrm{C}-\mathrm{C}, \mathrm{C}=\mathrm{C}, \mathrm{H}-\mathrm{H}$$ are $$414 \mathrm{~kJ}, 347 \mathrm{~kJ}, 615 \mathrm{~kJ}$$ and $$435 \mathrm{~kJ}$$ respectively is $$-$$ __________ $$\mathrm{kJ}$$
Answer
125
Explanation
$$\begin{aligned}
& \mathrm{C}_2 \mathrm{H}_4+\mathrm{H}_2 \longrightarrow \mathrm{C}_2 \mathrm{H}_6 \\
& \begin{aligned}
\Delta \mathrm{H} & =(615)+(435)-(347)-2(414) \\
& =615+435-347-828 \\
& =-125 \mathrm{~kJ}
\end{aligned}
\end{aligned}$$
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