Two moles of an ideal gas are expanded isothermally from 15 $\mathrm{dm}^3$ to $20 \mathrm{dm}^3$. If the…

Two moles of an ideal gas are expanded isothermally from 15 $\mathrm{dm}^3$ to $20 \mathrm{dm}^3$. If the amount of work done is $-6 \mathrm{dm}^3$ bar, find external pressure needed to obtain this work.
  1. $1.2 \times 10^5 \mathrm{~Pa}$
  2. $3.2 \mathrm{~Pa}$
  3. $8.1 \times 10^4 \mathrm{~Pa}$
  4. $2.4 \mathrm{~Pa}$

Solution

$\begin{aligned} & \mathrm{W}=- \text { Pext. }\left[\mathrm{V}_2-\mathrm{V}_1\right] \\ & -6 \text { bar. } \mathrm{dm}^3=- \text { Pext }[20-15] \\ & \text { Pext }=\frac{6}{5}=1.2 \text { bar } \\ & \left(1 \text { bar }=10^5 \mathrm{~Pa}\right) \\ & \text { Pext }=1.2 \times 10^5 \mathrm{~Pa}\end{aligned}$

Asked in: MHT CET 2021 (21 Sep Shift 2)

Practice more Chemical Thermodynamics questions on Aicharya