Types of Thermodynamics Processes


As we know that a system itself does not undergo any change rather, the state of the system changes. And "Whenever a system changes its state from one equilibrium state to another, the path of successive states through which the system has passed is called thermodynamic process". When there is an interaction between the system and the surrounding, the state of the system changes from one equilibrium to another. And these changes in the state of the system can be fast or slow and large or small. 
Thermodynamic processes are of two types namely "Quasi-static process" and "Non-quasistatic process". These processes are further classified into two categories "Reversible and Irreversible", as shown in the figure. Let's understand about them;

Reversible processes
"A process will be a reversible process when its direction can be reversed at any point by an infinitesimal change in external conditions" (Or we can say that a thermodynamics process would be called a reversible process when the process can be reversed in such a way that both the system and the surroundings return to their original state and no other changes occur anywhere in the universe).
No process like reversible processes exists in reality. Thus, reversible processes are an idealization of real processes. Due to reversibility, the process reaches in equilibrium. It proceeds in both the directions.
For Example- 
1. Water to ice or ice to water conversion is an example of reversible process,
2. Bernoulli equation is also an example of reversible process, 
3. A collision between two billiard balls is also an example of reversible process, etc.

Points To Be Remember 
➛ During a reversible process, all changes in the state of the system are in thermodynamic equilibrium with each other.
➛ "A process which is quasi-static and friction-less is called a reversible process".

Irreversible processes
"A thermodynamics process would be called as an irreversible process when the process can not be reversed in such a way that both the system and the surroundings return to their original state without any change in external conditions" (Or the thermodynamic process which can not be reversed back to its original state is known as irreversible process). These reactions occur in only one direction.
All spontaneous processes (spontaneous processes are those processes that occur at any instant in time) are irreversible in nature.
For Example- 
Diffusion, Electricity flow through resistance, Conversion of milk into curd, Heat transfer from hot body to cold body, Waterfall, Combustion of fuel, Burning of a paper, etc.
From the above figure, we can say that the process can not be reversed back from equilibrium state-2 to equilibrium State-1. 

Points To Be Remember
➛In the case of an irreversible process, the state of equilibrium cannot be achieved at any moment.
➛In general all types of processes occurring in nature i.e. natural processes are irreversible.
➛There are three types of irreversibility;
    • Internal irreversibility 
    • External irreversibility
    • Chemical irreversibility

Quasi-static Or Non-quasistatic Processes
"A process is said to be a Quasi-static process if the system is in equilibrium with itself or its surroundings at each and every point in the process path. i.e. at each and every intermediate stage, equilibrium exists between system and surrounding or with system itself". These processes happen very slowly. A quasi-static process is a succession of thermodynamics equilibrium states. These processes are not possible in nature so all natural processes are "Non-quasistatic". 
Some of the example of quasi-static processes are- Adiabatic process, Isothermal process, Isobaric process, Isochoric process and Polytropic process, etc.

Points To Be Remember
☛ "A quasi static process is a process carried out very very slowly, in an attempt to reach as close as possible to a reversible process".
☛ "The process may be quasistatic if it is carried out very slowly, but it can never be reversible because some of the compressive work is lost to friction and dissipated as heat".
☛ All natural processes are non-quasistatic.
☛Thermodynamic processes are mainly of two types, quasi-static and non-quasistatic. Let us see the difference between quasi-static and non-quasistatic process with the help of a curve;
"Between two states A and B, two types of processes take place. First, a quasi-static process in which the system passes through all states (or all the intermediate states are known), so the process path is drawn between A and B. Whereas the second, non-quasistatic in which intermediate states are not known, only the initial and final states are known so the process path between A and B is not drawn. All natural processes are non-quasistatic".


Hope you have found this article helpful!!
Let me know what you think about TYPES OF THERMODYNAMICS PROCESSES. Feel free to comment if you have any queries.!!

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