Isothermal and Adiabatic Process

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Difference Between Isothermal and Adiabatic Process

The word ‘isothermal’  means constant temperature. An isothermal process is a process occurring at a constant temperature.

The word ‘adiabatic’ means isolated from surroundings. Adiabatic process means a process that neither allows the heat to transfer inside nor let the heat out of the system.

For example, a reaction that takes place in a Dewar Flask is adiabatic. 

In this article, we will discuss adiabatic and isothermal, distinguish between isothermal and adiabatic processes, isobaric isochoric isothermal and adiabatic processes, and understand the process of isothermal adiabatic in detail.


Adiabatic and Isothermal

Now, we will understand the difference between adiabatic and isothermal:

Thermodynamics uses the concepts of the isothermal process, isochoric process, isobaric process, and adiabatic process to explain the behaviour of a thermodynamic system and its relationship to the temperature changes. 

An isothermal process is a process that happens when there are no variations in the temperature of the system, but other parameters (volume, pressure) regarding the system can be changed accordingly. 

Adiabatic process describes a process that remains aloof of its surroundings. It is a process in which no heat transfer occurs between a system and its surroundings. Here, the temperature of the system can vary in order to avoid any heat transfer. This indicates that the main difference between isothermal and adiabatic processes is that the isothermal process takes place under constant temperature whereas the adiabatic process occurs under changing temperature.

Now, let’s Compare Isothermal And Adiabatic Process in a tabular form to understand isothermal and adiabatic processes:


Difference Between Isothermal Process and Adiabatic Process

Isothermal Process

Adiabatic Process

Transfer of heat occurs in this process.

No heat goes inside or leaves the system.

At a given volume of the substance, the pressure remains high.

At a given volume of the substance, the pressure remains low.

In an isothermal process, the temperature remains invariant.

The temperature varies because of the internal system changes.

Heat can be added or released to the system to keep the temperature constant.

There is no addition of heat nor the release of the heat because maintaining constant temperature doesn’t matter here.

The isothermal process has a slower transformation flow.

The adiabatic process has a faster transformation flow.

In an isothermal system, work done is because of the change in the net heat content of the system.

In an adiabatic process, the work done is because of the change in internal energy.


Now, we will understand a bit more about isobaric isochoric isothermal and adiabatic processes:


Adiabatic Isothermal Isobaric Isochoric

Adiabatic Process

An adiabatic process is a thermodynamic process that can take place without any heat transfer between a system and its surrounding. Here, neither heat nor energy is not transferred into or out of the system. Therefore, in an adiabatic process, the only way the energy transfer takes place between a system and its surrounding is the work.

An adiabatic process can be quickly maintained by doing the process. For example, if we quickly press the piston in a cylinder filled with gas, there is not enough time for the system to transfer heat energy to the surroundings. In adiabatic processes, the work done by the system alters the internal energy of the system.

The below diagram shows the adiabatic process:


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Isothermal Process

An isothermal process is a thermodynamic process that takes place at a constant temperature. It means that an isothermal process occurs in a system where the temperature remains constant. However, to keep the temperature of the system constant, heat must be transferred into the system or shifted out of the system.

Apart from that, many factors of the system also vary during the continuation of an isothermal process such as internal energy. To maintain the temperature of the system, it can be kept in a tight cylinder. Then, by regulating the temperature of the cylinder, we can control the temperature of the system to an optimal level.

Below are the examples of the isothermal process:

  1. A phase change of matter

  2. Melting of matter, and

  3. Evaporation, etc. 


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A common industrial use of the isothermal process is the Carnot heat engine

To maintain the temperature of the system, work should either be done on the system or be done by the system on the surrounding; doing work on the gas increases the internal energy, which, in turn, increases the temperature. 

However, if the temperature rises more than the required range, then work is done by the system on the surrounding. However, when the temperature of the system decreases, the energy is released to the surroundings in the form of heat.


Isobaric Process

An isobaric process has the word ‘bar’, where the bar is the unit of pressure. Another three letters added ‘iso’ make a process called the isobaric process. An isobaric process is a process that takes place under constant pressure.


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Isochoric Process

The word ‘choric’ in isochoric stands for volume. An isochoric process is one that takes place at a constant volume.

If the work done, i.e., W = PΔV

At constant volume, ΔV =  0, i.e., no work is done by the system.

FAQ (Frequently Asked Questions)

1. Define the Thermodynamic Process.

Ans: A process occurs when the system changes from one set of values of its physical properties to another. The system reverts to the original state when all of its macroscopic physical properties regain their original values.

Heat transfer and work are two core processes that alter the state of thermodynamic equilibrium. A quasi-static process is one in which the system changes so slowly that each succeeding state through which it passes remains at equilibrium. 

All the reversible processes occur very slowly or are quasi-static in nature. An equilibrium state is a resting state. During a reversible process, the system can deviate from equilibrium by an infinitesimal amount.

There are other thermodynamic processes in equilibrium thermodynamics, viz: adiabatic, isochoric, and isobaric; where these processes are considered the thermodynamic variable that is kept constant.

2. What is an Isothermal Constant? State the Formula For the Isothermal Constant.

Ans: Isothermal Compression is the change in the volume of a system when the temperature is constant. It helps us determine the relationship between the pressure and density when the gas undergoes the compression process.

 For ideal gases, when the temperature is kept constant, the internal energy of the system also remains constant, so Δ U = 0. 

The First Law of Thermodynamics states that Δ U = Q + W, it follows that for the compression or expansion process to occur Q = − W for ideal gases. 

Though the isothermal compression process is a useful concept that determines the compressible attributes of a reservoir; however, is just a theoretical concept, and has no place in practical work.