Give real-world examples of nearly reversible processes

In classical thermodynamics, a truly reversible process is an idealization; all real processes have some dissipation (friction, finite temperature differences, resistance) and occur at finite rates, so they are irreversible. However, if a process is conducted very slowly and dissipative effects are minimized, it can be nearly reversible.

Examples that approximate reversibility:

• Slow phase changes: Ice–water mixture at 0 °C in an insulated container. Adding/removing an infinitesimal heat melts/freezes an infinitesimal amount while staying near equilibrium.
• Quasistatic, frictionless expansion/compression: A well-lubricated piston–cylinder moved extremely slowly so pressure and temperature remain uniform. (Ideal engine cycles assume this.)
• Elastic deformation of an ideal solid: Very slow loading/unloading of a perfectly elastic spring (ignoring internal friction/hysteresis) so it returns to its original state.
• Heat transfer with infinitesimal temperature difference: Thermal contact between bodies at nearly the same temperature (ΔT → 0) so the heat flow is arbitrarily slow.
• Near-equilibrium galvanic cell: Charging/discharging a battery at near-zero current so the cell operates close to its equilibrium potential.