IRREVERSIBLE PROCESS: A Process that cannot be retraced back in opposite direction is called an irreversible process”.In the irreversible process the system does not pass through the same intermediate states as in direct process, even If the same initial state is reached.
During this process the system may undergo several intermediate states of equilibrium. If this process is made to proceed in reverse direction, the system does not pass through the same intermediate states as in direct process. Examples:Example 1: In the process of rubbing out hands, heat is produced, increasing the temperature of the hands. The mechanical work done against friction is converted into heat. But in the reverse process, we cannot make the hands to move in same way on heating them. Example 2: Consider a process of mixing up two gases which do not react with each other. The two gases exist in two different equilibrium states. In the process of mixing them at constant temperature in a cylinder, the mixture attains a new state in thermodynamic equilibrium. The pressure of the mixture is greater than the individual pressures and possess same volume. In the reverse direction the gases cannot be separated to their initial conditions by decreasing the pressure.

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