Rarely Tested

Work Done in Thermodynamics

### Formula:

$$w=-P_{ext}\Delta V$$

### Terminologies:

- w β†’ Work done during expansion or compression.

- $$P_{ext}$$ β†’ External pressure acting on the system.

- Ξ”V β†’ Change in volume.

- Expansion β†’ Increase in volume of system.

- Compression β†’ Decrease in volume of system.

### Usage:

- Used to calculate work done when external pressure is constant.

Question 1

An ideal gas $$(0.5\ \mathrm{mol})$$, initially at $$2$$ bar pressure, is compressed at a constant temperature of $$600\ \mathrm{K}$$ in two steps: first, against a constant external pressure of $$P$$ bar $$(2 \lt P \lt 8)$$, and then against constant external pressure of $$8$$ bar. At each step, the compression is stopped only when the pressure of the gas becomes equal to the external pressure. The total work done on the gas in these steps is $$W$$. Considering all possible values of $$P$$ $$(2 \lt P \lt 8)$$ and taking the gas constant as $$R$$ (in $$\mathrm{J\ K^{-1}\ mol^{-1}}$$), the minimum value of $$|W|$$ (in $$\mathrm{J}$$) is

Go back to topics

Join CAT 2026 course by 5-Time CAT 100%iler

Start your IIM journey with the right preparation and crack CAT 2026.