What are the differences between reversible and irreversible thermodynamic processes?

1 Reversible Processes

A reversible process is a theoretical idealization of a process that can be reversed by an infinitesimal change in a variable, such as pressure, temperature, or concentration. In a reversible process, the system and its surroundings are always in equilibrium, and no entropy is generated. A reversible process is also called an isentropic process, meaning that the entropy of the system and its surroundings remains constant. A reversible process represents the maximum possible efficiency and work output of a process.

2 Irreversible Processes

An irreversible process is a realistic approximation of a process that cannot be reversed by any finite change in a variable. In an irreversible process, the system and its surroundings are not in equilibrium, and entropy is generated. An irreversible process is also called a dissipative process, meaning that some energy is dissipated as heat or friction and cannot be recovered. An irreversible process represents the actual efficiency and work output of a process, which is always lower than the reversible case.

3 Factors Affecting Reversibility

There are many factors that can make a process irreversible, such as friction, heat transfer, mixing, chemical reactions, electrical resistance, and turbulence. These factors introduce irreversibilities or losses that reduce the efficiency and work output of a process. The degree of irreversibility can be quantified by the entropy generation, which is the difference between the entropy change of the system and its surroundings in an irreversible process and a reversible process. The entropy generation is always positive or zero, never negative.

4 Examples of Reversible Processes

Although no real process is perfectly reversible, some processes can be approximated as reversible under certain conditions. For example, a reversible compression or expansion of an ideal gas is a process where the pressure and volume of the gas change slowly and in equilibrium with the surroundings, and no heat is transferred. Another example is a reversible heat transfer between two objects at the same temperature, where no temperature gradient or heat loss occurs.

5 Examples of Irreversible Processes

Most real processes are irreversible to some extent, due to the presence of irreversibilities or losses. For example, an irreversible compression or expansion of a gas is a process where the pressure and volume of the gas change rapidly and out of equilibrium with the surroundings, and heat is transferred to or from the surroundings. Another example is an irreversible heat transfer between two objects at different temperatures, where a temperature gradient and heat loss occur.