Difference between Quasi-static and Reversible process

As we know that a system itself does not undergo any change rather, the state of the system changes. And "When 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". 
In this, we study about two types of processes which are not really possible in nature and these are: "Reversible Process" or "Quasi-static process". Both are the idealization case of real processes.

The line that alone distinguishes between reversible and quasi-static processes, that is;
"All reversible processes are quasi-static processes but not all quasi-static processes are reversible processes".
Any system that involves dissipation of energy as heat, whether by friction, vibration, or any other mechanism, cannot be reversible even if it is quasistatic. Therefore, a 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.

Reversible process
"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). 
For example- expansion of a gas in a piston/cylinder arrangement is an example of reversible process In which first the gas (or system) expands and does some work on the surrounding. And then later some work is done on the gas (or system) by the surrounding, so that it gets compressed and comes back to its initial position.
➛ Let us understand this (or reversible process) through a diagram;
The above diagram shows a reversible process. From this diagram, it can be understood what a reversible process is??
"This diagram tells us that whenever a system changes its state from one to another (say; State-1➝ State-2 , Similarly; State- 2➝3 , State- 3➝4 and State- 4➝1), a process takes place between them. And when the system changes its state in such a way that the system and its surroundings return to their initial states without any change in the universe (say; from State- 1➝2 & 2➝3 & 3➝4 & State- 4➝1) , then the process is called reversible process". 
➛ Reversible process takes infinite time for completion. Hence, these processes are very slow.
➛ In reversible processes, the system and its surroundings are in equilibrium with each other in every state.
➛ By carrying out processes very slowly, we can reach "reversibility".

Quasi-static process
"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". This process happens very slowly. A quasi-static process is a succession of thermodynamics equilibrium states. This process is not possible in nature therefore all processes in nature are "Non-quasistatic". 
➛ Quasi-static process is an idealization of real processes.
➛ This process happens slowly enough so that the system remains in internal equilibrium at all the time.
➛ Some of the example of quasi-static processes are- adiabatic process, isothermal process, isobaric process, isochoric process and Polytropic process etc. 
➛ Quasi-static process: An infinitely slow process such that the system undergoes changes in its variables (P,V,T) so slowly that it continues to be in its thermal, mechanical and chemical equilibrium with its surroundings all the time and at all points. ( It is a hypothetical construct)


Hope you have found this article helpful!!
Let me know what you think about REVERSIBLE AND QUASI-STATIC PROCESS. Feel free to comment if you have any queries.!!

Comments

Post a Comment

Most Viewed Posts

Zeroth Law Of Thermodynamic: The Thermal Equilibrium Law

Image
In thermodynamics, we will see two types of walls. One is the Diathermic wall and the other is the adiabatic wall. Let us now go through them one by one.  • So the first is the Diathermic wall- " A Diathermic wall is a wall that allows the easy exchange of heat between two bodies (or between two systems or between system and surrounding) but does not allow the exchange of mass between them ". This means that it is a good conductor of heat. It is sometimes called as metallic wall because it is made of metal. • While the other is the adiabatic wall- " An Adiabatic wall is that wall which neither allows exchange of heat nor mass between two systems (or between system and surrounding) ". Since there is no exchange of heat and mass between the system and its surroundings, the system remains insulated from its surroundings. ➛ That's why whenever we separate the two systems by an adiabatic wall, then there is no concept of equilibrium between them. But whenever we sep...
Read more

Characteristics Of Entropy

Image
Entropy is an intrinsic property of a substance and is not affected by the external position of a system or its motion relative to other systems. It is a measure of the randomness of the system. Thus, the higher the randomness of the system, the higher the entropy of the system and the lower the randomness of the system, the lower the entropy of that system. Entropy   " Entropy is defined as a measure of the system's thermal energy that is incapable of doing work ". It is a state function.  For Example Heat is a form of energy that is incapable of doing work. Therefore, the more heat added to the system (or tranfer from the system), the higher (or the lower) will be its entropy.  The formula for change in entropy is given by the equation;                      ➩ ∆S = ∆Q/T For a reversible process, the change in entropy is given as; The Total Change In Entropy Entropy change is zero at equilibrium condition or whenev...
Read more

Reversed Carnot Cycle

Image
We have already discussed the concept of “ Carnot Cycle ”   & “ Its Efficiency ” and we have also seen the concept of “ Carnot Theorem And Its Explanation ” in our previous post. As we have already discussed that the Carnot Cycle is a reversible cycle and every process in the Carnot cycle is a reversible process. Therefore, every process of the Carnot cycle can be reversed. And the cycle can be operated in the opposite direction as well. In this article, we're interested in learning more about the reversed Carnot cycle, also known as the reversed Carnot heat engine cycle. Reversed Carnot Heat Engine It is important to note that if a reversible process is reversed, all related energy types—such as heat energy or work energy—will have the same magnitude but the direction of their interaction with matter will be changed. Let us first look at the Reverse Carnot Heat Engine  cycle here; The reversed Carnot heat engine cycle is depicted in the following figure. According to the...
Read more