Expansion work

Definition

Expansion work is the work done by a system when it expands against an external pressure. It often occurs during processes where gases are involved, such as in chemical reactions or physical changes.

5 Must Know Facts For Your Next Test

1. Expansion work is calculated using the formula $W = -P_{ext} \Delta V$, where $P_{ext}$ is the external pressure and $\Delta V$ is the change in volume.
2. The sign of expansion work is negative because the system loses energy to do the work on the surroundings.
3. In an isothermal process for an ideal gas, expansion work can be calculated using $W = -nRT \ln(\frac{V_f}{V_i})$, where $n$ is the number of moles, $R$ is the gas constant, and $V_f$ and $V_i$ are final and initial volumes respectively.
4. Expansion work only occurs if there is a change in volume during a process.
5. Reversible processes perform maximum expansion work compared to irreversible processes.

Review Questions

• How do you calculate expansion work in terms of external pressure and volume change?
• Why is the sign of expansion work negative?
• What formula would you use to calculate expansion work for an ideal gas undergoing an isothermal process?

Related terms

Enthalpy: A thermodynamic quantity equivalent to the total heat content of a system. It is equal to internal energy plus the product of pressure and volume.

Internal Energy: The total energy contained within a system, including both kinetic and potential energy at the molecular level.

Isothermal Process: A thermodynamic process that occurs at a constant temperature throughout.