A fish swimming in water body when taken out from the water body is covered with a film of water of weight 36 g. When it is subjected to cooking at 100$^\circ$C, then the internal energy for vaporization in kJ mol$-$1 is ___________. [nearest integer]
[Assume steam to be an ideal gas. Given $\Delta$vapH$^\Theta$ for water at 373 K and 1 bar is 41.1 kJ mol$-$1 ; R = 8.31 J K$-$1 mol$-$1]
Answer (integer)
38
Solution
$\underset{36 \mathrm{~g}}{\mathrm{H}_{2} \mathrm{O}}(\ell) \longrightarrow \underset{36 \mathrm{~g}}{\mathrm{H}_{2} \mathrm{O}}(\mathrm{g})$ (evaporation)
<br/><br/>
$$
\begin{aligned}
\mathrm{n}_{\mathrm{H}_{2} \mathrm{O}} &=\frac{36}{18}=2 \quad \Delta \mathrm{n}_{\mathrm{g}}=1-0=1 \\\\
\Delta \mathrm{U}_{\text {vap }} &=\Delta \mathrm{H}_{\text {vap }}-\Delta \mathrm{n}_{\mathrm{g}} \mathrm{RT} \\\\
&=41.1-(1) \times 8.31 \times 10^{-3} \times 373 \\\\
&=41.1-3.099 \\\\
&=38 \mathrm{~kJ} / \mathrm{mol}
\end{aligned}
$$
About this question
Subject: Chemistry · Chapter: Thermodynamics · Topic: Zeroth and First Law
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