Certain amount of an ideal gas is expanded isobarically to double its volume. Work obtained in the process is $-20 \mathrm{kJ}$. If same expansion in volume is carried out isothermally irreversibly in single step, then, calculate the magnitude of work ( in kJ).

Let initial          Final state                  Final state
State                  (Isobaric)                  (Isothermal)

$P\to$                    $P$                                 $\frac{P}{2}$

$V\to$                   $2V$                              $2V$

$\underset{\mathrm{isobaric}}{W}$$=-P [2V-V]$

             $$\begin{gathered} =-PV=20 \mathrm{KJ} \\ \mathrm{PV}=20 \end{gathered}$$

$\underset{\mathrm{isobaric}}{W}$$=-P_{ext}[2V-V]; P_{ext}=\frac{P}{2}$