Q40 / 180 · KCET 2025 · Chemistry

Which one of the following reactions has $\Delta \mathrm{H}=\Delta \mathrm{U}$ ?

  • A
    $\mathrm{CaCO}_3(\mathrm{~s}) \xrightarrow{\Delta} \mathrm{CaO}(\mathrm{s})+\mathrm{CO}_2(\mathrm{~g})$
  • B
    $\mathrm{C}_6 \mathrm{H}_6(\mathrm{I})+\frac{15}{2} \mathrm{O}_2(\mathrm{~g}) \longrightarrow 6 \mathrm{CO}_2(\mathrm{~g})+3 \mathrm{H}_2 \mathrm{O}(\mathrm{I})$
  • Correct answer
    C
    $2 \mathrm{HI}(\mathrm{g}) \rightleftharpoons \mathrm{H}_2(\mathrm{~g})+\mathrm{I}_2(\mathrm{~g})$
  • D
    $\mathrm{N}_2(\mathrm{~g})+3 \mathrm{H}_2(\mathrm{~g}) \rightleftharpoons 2 \mathrm{NH}_3(\mathrm{~g})$

Solution

$\begin{aligned} & \Delta \mathrm{H}=\Delta \mathrm{U}+\Delta \mathrm{ng} \mathrm{RT} \\ & \text { For } 2 \mathrm{HI}_{(\mathrm{g})} \rightleftharpoons \mathrm{H}_{2(\mathrm{~g})}+\mathrm{I}_{2(\mathrm{~g})} \\ & \Delta \mathrm{ng}=0 \\ & \therefore \Delta \mathrm{H}=\Delta \mathrm{U}\end{aligned}$

Hence, the correct answer is option: 'C'.

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