Entropy is defined as the magnitude of the irreversibilities of a process. Entropy is the disorder of molecules within a system. If the system is closed, entropy is produced if the process is irreversible. If the system is subjected to expansions or energy transfer, the entropy increases.
A process is reversible if the system and its surroundings are returned to their initial states. In a quasi-static process it is characterized by being a reversible process in which there are no irreversibilities. The entropy in this system is constant in the system.
