A quasi-static process is a thermodynamic process that happens infinitely slowly, so the system remains in or very close to thermodynamic equilibrium at every step throughout the process.

Key points about a quasi-static process:

• The process proceeds so slowly that the system is always nearly balanced internally.
• There are no sudden changes; pressure, temperature, and other properties are well-defined at every point.
• Because the system stays close to equilibrium, the process is often considered reversible or very close to reversible.
• It’s an idealization used in thermodynamics to analyze processes like slow compression, expansion, heating, or cooling.

Why is it important?

Real processes happen at finite speeds and often away from equilibrium, but assuming a quasi-static process lets us apply equilibrium thermodynamics and calculate work, heat transfer, and changes in state variables more easily.