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Consider the following processes
$$
\begin{array}{l}
\Delta \mathrm{H}(\mathrm{kJ} / \mathrm{mol}) \\
\quad \frac{1}{2} \mathrm{~A} \longrightarrow \mathrm{B}+150 \\
3 \mathrm{~B} \longrightarrow 2 \mathrm{C}+\mathrm{D}-125 \\
\mathrm{E}+\mathrm{A} \longrightarrow 2 \mathrm{D}+350
\end{array}
$$
For $\mathrm{B}+\mathrm{D} \longrightarrow \mathrm{E}+2 \mathrm{C}, \Delta \mathrm{H}$ will be
Options:
$$
\begin{array}{l}
\Delta \mathrm{H}(\mathrm{kJ} / \mathrm{mol}) \\
\quad \frac{1}{2} \mathrm{~A} \longrightarrow \mathrm{B}+150 \\
3 \mathrm{~B} \longrightarrow 2 \mathrm{C}+\mathrm{D}-125 \\
\mathrm{E}+\mathrm{A} \longrightarrow 2 \mathrm{D}+350
\end{array}
$$
For $\mathrm{B}+\mathrm{D} \longrightarrow \mathrm{E}+2 \mathrm{C}, \Delta \mathrm{H}$ will be
Solution:
2133 Upvotes
Verified Answer
The correct answer is:
$-175 \mathrm{~kJ} / \mathrm{mol}$
$$
\begin{array}{l}
\frac{1}{2} A \rightarrow B ; \Delta \mathrm{H}=150 \mathrm{~kJ} / \mathrm{mol}...(i) \\
3 B \rightarrow 2 C+D ; \Delta H=-125 \mathrm{~kJ} / \mathrm{mol}...(ii) \\
E+A \rightarrow 2 D ; \Delta H=+350 \mathrm{~kJ} / \mathrm{mol}...(iii) \\
\text { By }[2 \times(\mathrm{i})+(\text { ii })]-(\text { iii }), \text { we have } \\
B+D \rightarrow E+2 C \\
\therefore \Delta H=150 \times 2+(-125)-350 \\
=-175 \mathrm{~kJ} / \mathrm{mol}
\end{array}
$$
\begin{array}{l}
\frac{1}{2} A \rightarrow B ; \Delta \mathrm{H}=150 \mathrm{~kJ} / \mathrm{mol}...(i) \\
3 B \rightarrow 2 C+D ; \Delta H=-125 \mathrm{~kJ} / \mathrm{mol}...(ii) \\
E+A \rightarrow 2 D ; \Delta H=+350 \mathrm{~kJ} / \mathrm{mol}...(iii) \\
\text { By }[2 \times(\mathrm{i})+(\text { ii })]-(\text { iii }), \text { we have } \\
B+D \rightarrow E+2 C \\
\therefore \Delta H=150 \times 2+(-125)-350 \\
=-175 \mathrm{~kJ} / \mathrm{mol}
\end{array}
$$
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