An isothermal process is a thermodynamic process that occurs at a constant temperature. During this process, although heat may flow into or out of the system, the internal energy remains unchanged because temperature is directly related to internal energy for ideal gases.
To maintain a constant temperature, any energy added as heat must be exactly balanced by work done by or on the system. For example:
- In isothermal expansion, a gas absorbs heat and does work on its surroundings, but its temperature doesn’t increase.
- In isothermal compression, the gas is compressed, work is done on it, and it releases heat to maintain the same temperature.
Isothermal processes are idealizations often used to simplify analysis in:
- Heat engines and refrigeration cycles,
- Ideal gas law applications,
- Phase changes like melting or boiling, where temperature stays constant while energy is added or removed.
These processes are typically slow, allowing heat exchange with the surroundings to maintain thermal equilibrium. Isothermal conditions are essential for understanding many equilibrium-based systems in physics and engineering.