In a complete cycle, there are four processes; reversible isothermal expansion where the expansion of the piston cylinder and gas takes place at the same temperature. The second cycle is the reversible adiabatic expansion where the temperature of the gas drops because there is no heat transfer. At reversible isothermal compression, compression of the gas takes place at the same temperature by rejecting heat from the system. In the last step, reversible adiabatic compression, compression of the gas takes place and the temperature of the gas rises.