Notes on Reversible And Irreversible Processes

Introduction 

Every human activity takes place in an environment, which may be natural or artificial. From prehistoric times, humans have attempted to study the phenomenon around them. We first attempt to understand and describe the basic laws which govern natural phenomena. In our daily lives, we witness several changes like water boiling, iron rusting, ice melting, paper burning, fermentation, etc. From our observations, we know that processes like rusting and fermentation are not reversible in natural circumstances.

In this article, we will look at processes which are reversible and irreversible.

Reversible Processes

Reversible processes occur when a system returns to its original state after being disturbed. A classic example of this is the water cycle. A classic example is melting ice and vice versa. Water is originally in liquid condition, then freezes to produce ice, which melts again to give water when heated.

Students should be aware that a reversible process involves two processes. While in the first process, particles change into another form, the reverse reaction occurs in the second process, with the results returning to the beginning stage.

As a result, comprehending this will aid in further diving into the distinction between reversible and irreversible processes. For example, we can quickly push back the piston when the ideal gas expands in a vacuum or doubles its initial volume and restores its temperature and pressure by extracting some gas’s heat.

What are Irreversible Processes, and how do they work?

Irreversible processes cannot be reversed or at least cannot be reversed without the great expense of time and money. Irreversible processes are controlled by economic considerations (costs), and these considerations usually eliminate one or more variables in the balanced equation. This is because if any of the variables were eliminated, it would destroy the balance of the reaction, and the system would be unable to sustain itself.

For example, in an oil refinery plant where crude oil is converted into valuable products such as gasoline, kerosene, etc., many steps take place as each stage in the process consumes certain portions of the crude oil and turns out certain by-products. Each step in this process can never be reversed because if any one of these steps were eliminated, it would destroy the balance of the reaction.

Let’s take another example. Consider the situation of a car engine that has travelled a particular distance while using a specific amount of fuel. The fuel burns to provide energy to the engine, producing smoke and heat energy in the process. We will never be able to regain the energy that the fuel has lost, nor will we ever be able to restore it to its former state and thus destroy what is called “economy”. 

As a result, depending on their ability to return to their original form from their final state, specific processes are reversible while others are irreversible. Relative motion with friction, heat transfer throttling, diffusion and irreversible processes include the flow of electricity across a resistance.

Practically every situation is an example of an irreversible process since the system and its nature cannot be restored to their initial states simultaneously. Because it is considered a natural phenomenon, the small gradient between the states in the natural process indicates that the process is irreversible.

When heat travels from one substance to another, the temperature difference between the two is finite. More importantly, at no point during the process is the system likely to be in equilibrium or a well-defined state. This is known as irreversibility.

Difference between reversible Process & irreversible process 

1. A reversible process is a process that can be reversed to obtain the initial state of the system whereas an irreversible process is a thermodynamic process that cannot be reversed to obtain the initial state of a system
2. Reversible can be reversed and were as irreversible process cannot be reversed
3. In reversible process, infinite change occurs in the system, and in the case of the Irreversible process, finite changes occur in the system
4. There is an equilibrium between the initial state and the system’s final state. However, in an irreversible process, there is no equilibrium in the system

Thermodynamic Processes: Reversible and Irreversible

Thermodynamic processes can be further classified as either reversible or irreversible. In a reversible process, the system changing can go back to its original state after the process has been completed. Reversible processes occur in many everyday situations:

For example, you can walk on ice and melt it but it will re-freeze after you have walked on it. The melting rate is slow compared to the rate at which the ice freezes. This is a reversible process.                  

Conclusion:  

A reversible process is one in which the system and its surroundings can both return to their original states by taking a  different path. An irreversible process is one in which the system and its environment cannot return to their original states together. The second law of thermodynamics results in the irreversibility of any natural process. These processes are natural or manmade depending upon the nature of the process.