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 (integer)
125
Solution
<p>$$\begin{aligned}
& \mathrm{C}_2 \mathrm{H}_4+\mathrm{H}_2 \longrightarrow \mathrm{C}_2 \mathrm{H}_6 \\
& \begin{aligned}
\Delta \mathrm{H} & =(615)+(435)-(347)-2(414) \\
& =615+435-347-828 \\
& =-125 \mathrm{~kJ}
\end{aligned}
\end{aligned}$$</p>
About this question
Subject: Chemistry · Chapter: Thermodynamics · Topic: Zeroth and First Law
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