JEE Main 2007 — Thermodynamics (C) Question with Solution
JEE Main 2007
Question
Assuming that water vapour is an ideal gas, the internal energy when of water is vapourised at pressure and , (Given: Molar enthalpy of vapourization of water at and and ) will be
Choose an option
Show full solutionCorrect option: C
Correct answer
C
Step-by-step explanation
$\begin{aligned}
& \mathrm{H}_2 \mathrm{O}(\ell) \stackrel{\text { vaporisation }}{\longrightarrow} \mathrm{H}_2 \mathrm{O}(\mathrm{g}) \\
& \Delta \mathrm{n}_{\mathrm{g}}=1-0=1 \\
& \Delta \mathrm{H}=\Delta \mathrm{U}+\Delta \mathrm{n}_{\mathrm{g}} \mathrm{RT} \\
& \Delta \mathrm{U}=\Delta \mathrm{H}-\Delta \mathrm{n}_{\mathrm{g}} \mathrm{RT} \\
& =41-8.3 \times 10^{-3} \times 373 \\
& =37.9 \mathrm{~kJ} \mathrm{~mol}^{-1}
\end{aligned}$
Hence, (C) is correct.
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