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.


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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.

Key Takeaways

  1. Adiabatic processes involve no heat exchange with the surroundings, resulting in temperature changes.
  2. Isothermal processes occur at a constant temperature, requiring heat exchange with the environment to maintain equilibrium.
  3. Adiabatic processes are often associated with rapid expansion or compression, while isothermal processes are common in slower, controlled systems.

Adiabatic vs Isothermal

An adiabatic process is a thermodynamic process that occurs without any transfer of heat between the system and its surroundings. An isothermal process is a thermodynamic process which occurs at a constant temperature, with heat being transferred to or from the system to maintain this temperature.

Adiabatic vs Isothermal

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A thermodynamic process, also known as an Isocaloric process, the 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

Parameters of ComparisonAdiabaticIsothermal
DefinitionA thermodynamic process happens between a system and its surroundings, with zero heat transfer.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 no final change in heat. In this process, the temperature varies, the pressure is low compared to the volume, and they reform so 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 cannot disappear.

The adiabatic process equation:

PVγ = constant

P is the system’s pressure, V is the system’s volume, and γ is the adiabatic index, 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.
  • Devices such as nozzles, compressors, and turbines are applied with adiabatic efficiency.
  • The pendulum oscillating in a vertical plane is one such popular adiabatic process example.

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 working 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 to maintain 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 than the volume, whereas, In the isothermal process, the pressure is more than 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. In the Isothermal process, the system is thermally isolated, hence requiring a closed system.
Difference Between Adiabatic and Isothermal
  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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