Question 6: Explain with examples reversible and irreversible processes.
The change in the state of a system by changing the state variables is called a process. The process occurs when the system exchange energy (in the form of heat or work) with its surrounding.
Processes may be of two types;
(1) Reversible Process
(2) Irreversible Process
A reversible process is one that can be retraced exactly in the reverse order without producing any changes in the surrounding.
In such a process, the system passes exactly through the same stages as in the direct process. The thermal and mechanical effects (for example, temperature and work) at each stage are exactly reversed. Therefore, if heat is absorbed in the direct process, it will be given out in the reverse process. Similarly, if work is done by the system in the direct process, work will be done on the system in the reverse process.
In practice, no actual change is exactly reversible. However, a very slowly occurring process can be considered reversible.
A process which cannot be retraced in the backward direction by reversing the controlling factors is called irreversible process.
Processes occurring with the dissipation of energy or involving friction are always irreversible.