A reversible process is a theoretical idealization that describes a system undergoing changes without any loss or dissipation of energy. In a reversible process, the system is in equilibrium at every stage of the process. One key requirement for a reversible process is that it must be quasi-static.
A quasi-static process, also known as a quasi-equilibrium process, is a process that occurs infinitesimally slowly and maintains equilibrium throughout. It involves a series of equilibrium states that the system passes through as it changes from the initial state to the final state. At each intermediate stage, the system is in equilibrium, meaning its properties such as pressure, temperature, and volume do not change abruptly.
The reason a reversible process is necessarily a quasi-static process is that for a process to be reversible, it must proceed in infinitesimally small steps, each of which is in equilibrium. This requirement ensures that the system is always very close to equilibrium, minimizing any deviations or imbalances that could result in irreversibilities or energy losses.
If a process occurs rapidly or non-equilibrium conditions are present, it will not be reversible. In such cases, the system will not have enough time to adjust to the changes occurring, and there will be imbalances or gradients within the system, resulting in energy losses or irreversible effects. Hence, a reversible process must be quasi-static to maintain equilibrium at all times and avoid dissipative effects.