For water at 100^ C and 1 , bar, _ vap H- _ vap U=...... 10^ 2 ,~… - Vidyadip

MCQ

For water at $100^{\circ} \mathrm{C}$ and $1\, bar,$

$\Delta_{\text {vap }} \mathrm{H}-\Delta_{\text {vap }} \mathrm{U}=...... \times 10^{2} \,\mathrm{~J}\, \mathrm{~mol}^{-1}$. (Round off to the NearestInteger)

$\left[\right.$ Use : $\left.R=8.31\, \mathrm{~J}\, \mathrm{~mol}^{-1}\, \mathrm{~K}^{-1}\right]$

[Assume volume of $\mathrm{H}_{2} \mathrm{O}(\mathrm{l})$ is much smaller than volume of $\mathrm{H}_{2} \mathrm{O}(\mathrm{g})$. Assume $\mathrm{H}_{2} \mathrm{O}(\mathrm{g})$ treated as an ideal gas]

A
$70$
B
$89$
C
$40$
✓
$31$

✓

Answer

Correct option: D.

$31$

d
$\mathrm{H}_{2} \mathrm{O}_{(\ell)} \rightleftharpoons \mathrm{H}_{2} \mathrm{O}_{(\mathrm{v})}$

$\Delta \mathrm{H}=\Delta \mathrm{U}+\Delta \mathrm{n}_{\mathrm{g}} \mathrm{RT}$

for $1\, mole$ waters;

$\Delta \mathrm{n}_{\mathrm{g}}=1$

$\therefore \Delta \mathrm{n}_{\mathrm{g}} \mathrm{RT}=1 \,\mathrm{~mol} \times 8.31\, \mathrm{~J} / \mathrm{mol}-\mathrm{k} \times 373\, \mathrm{~K}$

$=3099.63\, \mathrm{~J} \cong 31 \times 10^{2}\, \mathrm{~J}$

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