Difference Between Adiabatic and Isothermal

Though it is not a very common term, Thermodynamics is studied by everyone in their classes. The different processes that deal with energy conservation and the energy to do work are made familiar to us. Though we don’t realize their importance in real life, they help in many types of studies.

 Such two thermodynamic processes are Adiabatic and Isothermal, which have very different properties from each other.

Adiabatic vs Isothermal

The main difference between Adiabatic and Isothermal is that there is no heat transfer in the case of Adiabatic, whereas Isothermal permits the transfer of heat from the surroundings. The temperature during the adiabatic process changes as the variations takes place inside the system, whereas the Isothermal process has their overall temperature constant inside the system.

Adiabatic and Isothermal

A thermodynamic process, also known as an Isocaloric process, Adiabatic process doesn’t let the heat penetrate in the system. This leads to the lowering of pressure and variation in the temperature due to variations in the system. The gas also tends to cool down when expanding. It is opposite from that of Isothermal processes.

A thermodynamic process in which the temperature remains constant and there takes the place of heat transfer is known as the Isothermal Process. While the pressure is more in the comparison of volume, the rate of transformation is very slow in such types of processes. For the maintenance of the temperature, heat is either released or added from the surrounding.

Comparison Table Between Adiabatic and Isothermal

Parameters of ComparisonAdiabaticIsothermal
DefinitionA thermodynamic process happens between a system and surrounding, and the heat transfer is zero.A thermodynamic process in which the temperature remains constant.
TemperatureDue to variations in the process, the temperature changes.The temperature remains constant throughout the process.
Heat transferThere is no heat transfer in such a process.There is the transfer of heat in such processes.
NatureIn such processes, the transformations happen at a fast rate.In such processes, the transformations happen at a slow rate.
PressureIn comparison to volume, the pressure is less.In comparison to volume, the pressure is more.

What is Adiabatic?

Correlated to the First Law of thermodynamics, Adiabatic processes have no net heat transfer, and there is no final change in heat. In this process, the temperature varies, the pressure is low as compared to the volume, and they reform in such a way that the heat energy remains constant.

Most clearly seen in gases, the Adiabatic process is associated with the law of conservation of energy that says energy is neither created nor destroyed. So by this, it says, the heat energy present in the system will either do the work or will fluctuate the internal energy of the system or some merger of both. The heat just cannot disappear.

The adiabatic process equation:

PVγ = constant

Where P is the pressure of the system, V is the volume of the system, and γ is the adiabatic index where it is defined as the ratio of heat capacity at constant pressure Cp to heat capacity at constant volume Cv.

Some examples of Adiabatic processes are: 

  • When we put ice into the icebox, the heat is neither going out nor coming in.
  • A device such as nozzles, compressors, and turbines is applied adiabatic efficiency.
  • The pendulum oscillating in a vertical plane is one of such popular adiabatic process examples.

What is Isothermal?

A thermodynamic process in which the temperature of the system doesn’t change and remains constant even if the volume and pressure vary. It has a slow rate of transformation, and the heat can be changed to maintain the constant temperature inside the system.

This process serves as a base for the working of electrical power plants, heat engines, and many such modern times’ machines. Apart from it, its importance lies in many fields such as space science, geology, biology, planetary science, etc.

Some examples of Isothermal processes are:

  • One example which we use in daily life is a Refrigerator that works isothermally maintaining its internal temperature constant instead of various changes happening around it.
  • Some other examples are Carrot engines, heat pumps, etc., that work isothermally.

Main Differences Between Adiabatic and Isothermal

  1. In the adiabatic process, there is no transfer of heat takes place whereas, In the isothermal process, there is a change that takes place in case of heat transfer.
  2. In the adiabatic process, the temperature doesn’t remain constant and changes, whereas It is the opposite in isothermal, and the temperature remains constant.
  3. In an adiabatic process, there is no question of adding or releasing heat for maintaining temperature, whereas, In an isothermal process, the heat can be added or released to maintain a constant temperature.
  4. In the adiabatic process, the transformation rate is fast, whereas, in the Isothermal process, the transformation rate is slow.
  5. In the adiabatic process, the pressure is less as compared to volume, whereas, In the isothermal process, the pressure is more in comparison to the volume.
  6. In an adiabatic process, the internal energy of the system changes, whereas It doesn’t change in the isothermal process.
  7. In the adiabatic process, both open and closed systems can be used as the system is not thermally isolated, whereas, in the Isothermal process, the system is thermally isolated, and hence it requires a closed system.


These both terms of the thermodynamic processes we have came across in our chemistry classes. Both processes discussed have their behaviour that is poles apart. All the differences can be seen above, and one is able to distinguish between these two. 

The study of both these processes helps in understanding the temperature regulation in the body of living organisms. The examination of heat, temperatures, energy, and their relationship between them is very important when it comes to biological studies. It helps further in meteorology also. These studies helped us in day-to-day life also. So, It is of great use to know about them and how they work, the reason behind such processes.


  1. https://www.sciencedirect.com/science/article/pii/S0301462209001343
  2. https://www.sae.org/publications/technical-papers/content/972649/https://www.sciencedirect.com/science/article/pii/S0360319907006544
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