Question

what is a reversible versus irreversible path and why is a reversible path useful while being physically impossible. what makes a reversible path impossible?

Answer 1

When the system undergoes a change from its initial state to the final state, the system is said to have undergone a process. During the thermodynamic process, one or more of the properties of the system like temperature, pressure, volume, enthalpy or heat, entropy, etc. changes.

The process in which the system and surroundings can be restored to the initial state from the final state without producing any changes in the thermodynamics properties of the universe is called a reversible process.

Throughout the entire reversible process, the system is in thermodynamic equilibrium with its surroundings. Since it would take an infinite amount of time for the reversible process to finish, perfectly reversible processes are impossible

The irreversible process is also called the natural process because all the processes occurring in nature are irreversible processes. The natural process occurs due to the finite gradient between the two states of the system. For instance, heat flow between two bodies occurs due to the temperature gradient between the two bodies; this is in fact the natural flow of heat.