(1) Isothermal process and Adiabatic process.
Isothermal process :
1. In an isothermal process, the temperature of the system remains constant.
ΔT = 0
2. In this process, the system exchanges heat with the surroundings.
Q ≠ 0 (Closed system)
3. The total internal energy of the system remains constant.
4. In this process, the system is not thermally isolated.
5. In this process, Q = -W as ΔU = 0.
6. ΔH = 0.
Adiabatic process :
1. In an adiabatic process, the temperature of the system changes.
ΔT ≠ 0
2. In this process, the system does not exchange heat with the surroundings.
Q = 0 (Isolated system)
3. The total internal energy of the system changes.
ΔU ≠ 0
4. In this process, the system is thermally isolated.
5. In this process, W = ΔU.
6. ΔH ≠ 0.
(2) Reversible and irreversible processes.
Reversible process :
1. The process whose direction can be reversed at any stage by an infinitesimal increase in the opposing force is called a reversible process.
2. Such a process is not spontaneous and takes place infinitesimally slowly and takes infinite time for completion.
3. In this process, the thermodynamic equilibrium is always maintained between the system and the surroundings at every step.
4. The opposing force is infinitesimally less than the driving force.
5. It is an ideal or hypothetical process.
6. Maximum work can be derived from such a process.
Irreversible process :
1. The process whose direction cannot be reversed by an infinitesimal increase in the opposing force is called an irreversible process.
2. Such a process is spontaneous and takes finite time for completion.
3. The thermodynamic equilibrium is attained only at the end of the process.
4. The opposing force is significantly less than the driving force.
5. It is a practical or real and spontaneous process.
6. Work derived from such a process is always less than the maximum work.
