MCQ
Assuming that water vapour is an ideal gas, the internal energy change $(\Delta U)$ when $1\, mol$ of water is vapourised at $1\, bar$ pressure and $100\,^oC,$ (given : molar enthalpy of vapourisation of water at $1\, bar$ and $373\, K = 41\, kJ\, mol^{-1}$ and $R = 8.3\, J\, mol^{-1}\, K^{-1}$) will be .............. $\mathrm{kJ\,mol}^{-1}$
  • A
    $41$
  • B
    $4.100$
  • C
    $3.7904$
  • $37.904$

Answer

Correct option: D.
$37.904$
d
$\Delta H=41\, k J\, m o l^{-1}$

$=41000 \mathrm{\,J} \mathrm{\,mol}^{-1}$

$T=100\,^{\circ} \mathrm{C}=273+100$

$=373 \,K, n=1$

$\Delta U=\Delta H-\Delta n R T$

$=41000-(2 \times 8.314 \times 373)$

$=37898.88 \mathrm{\,J} \mathrm{\,mol}^{-1}$

$=37.9 \mathrm{\,kJ} \mathrm{\,mol}^{-1}$

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