It is the path or operation by which a system changes from one state to another state.
1. Isothermal process:
The temperature of the system remains constant during each step.
T = constant => dT = 0
- For such change system should be contained in a perfectly conducting container.
- Perfect isothermal change is impossible but when a change is carried out very slowly approximate isothermal change occurs.
- It follows Boyle’s law.
- Work done in the isothermal process is graphically given by the area under the P-V curve.
- ∆H = nCp∆T and ∆H = nCv∆T
In isothermal process ∆T = 0
=> ∆H = 0 and ∆E = 0
Specific change at constant T is infinitely great in the isothermal process.
2. Adiabatic process:
There is no heat exchange between the system and surroundings.
q = constant
=> dq = 0
Perfectly adiabatic change is impossible but when a process is carried out very rapidly fairly
approximate adiabatic change occurs.
3. Isobaric process:
It is the system in which pressure of the system remains constant during each step.
P = constant , dp = 0
4. Polytropic process:
In this process heat capacity of the body remains constant.
Cp = constant and Cv = constant
=> dCp = 0 and dCv = 0
5. Quasistatic process:
The process in which the deviation from thermodynamic equilibrium is infinitesimal and all the states through which the system passes can be considered as equilibrium states.
6. Isochoric process :
When there is no change in the volume of the system during various operations the change is said to be isochoric.
V = constant => dv = 0
For example, the combustion of a substance in a bomb calorimeter is an isochoric process.
7. Cyclic process:
The process which brings back a system to its original state after a series of changes is called acyclic process.
As the E and H depend only on their states, E and H are constant.
So, dE = 0 and dH = 0