Question

Entropy change when 4 moles of an ideal gas expands reversibly from an initial volume of 1 $d{m}^3$ to a final volume of 10 $d{m}^3$ at a constant temperature of 298 K is

• A. $5705.8J{K}^{-1}$
• B. $76.58J{K}^{-1}$
• C. $38.29J{K}^{-1}$
• D. $-19.15J{K}^{-1}$

Answer 1

The correct option is B $76.58J{K}^{-1}$

$△S=\frac{q_{rev}}{T}$
For isothermal reversible change
$W=q_{rev}=2.303nRT\log \frac{V_2}{V_1}$
n = 4 moles, $V_1=1d{m}^3$ and $V_2=10d{m}^3$
$\therefore △S=2.303nR\log \frac{V_2}{V_1}$
$=2.303\times 4mol\times 8.314J{K}^{-1}mo{l}^{-1}\log \left(\frac{10}{1}\right)=2.303\times 4\times 8.314J{K}^{-1}\therefore △S=76.58J{K}^{-1}$