MCQ
Expansion of $1$ $mole$ of ideal gas is taking place from $2$ $litre$ to $8$ $litre$ at $300\,K$ against $1$ $atm$ pressure. Calculate $\Delta {S_{total}}$ in $J\,K^{-1}\,mol^{-1}$ 

(given $R = \frac{{8.3\,J}}\,{{mol - K}}$, $1$ $lit$ -$atm$ $=$ $100$  $J$ $ln$ $2$ $=$ $0.693$)

  • A
    $11.5$
  • B
    $13.5$
  • $9.5$
  • D
    $22.5$

Answer

Correct option: C.
$9.5$
c
$\Delta S_{\text {sys }}=R \ln \frac{V_{2}}{V_{1}}=8.3 \ln 4$

$=8.3 \times 2 \times 0.693$

$=11.5\,\mathrm{J} / \mathrm{mol}-\mathrm{K}$

$\Delta S_{\text {surr. }}=\frac{-q_{\text {sys }}}{T}=\frac{-P_{\text {ext }}\left(V_{2}-V_{1}\right)}{T}$

$=-\left(\frac{(8-2)}{300}\right) \times 100=-2 \frac{\mathrm{J}}{\mathrm{mol}-\mathrm{K}}$

$\Delta S_{\text {Total }}=11.5-2=9.5 \,\frac{\mathrm{J}}{\mathrm{mol}-\mathrm{K}}$

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