Question

Find the work done (in $kJ$) when one mole of the gas is expanded reversibly and isothermally from $5atm$ to $1atm$ at ${25}^{o}C$.

• A. $+4kJ$
• B. $-4kJ$
• C. $-0.4kJ$
• D. $+4kJ$

Answer 1

The correct option is B $-4kJ$

Work done in case of reversible isothermal process is given by

$w=-2.303nRTlog\frac{P_1}{P_2}$
Given : $P_1=5atm$
$P_2=1atm$
$n=1$
$T=25+273=298K$

$w=-2.303\times 1\times 8.314$ $\times 298$ $log\frac{5}{1}$
using $log5=0.693$
$w=-3.98kJ$ or $-4kJ$