Types of Thermodynamic Process: Cyclic, Isobaric, Isochoric, Isothermal, Adiabatic Processes & Equations

Types of Thermodynamic Process: Cyclic, Isobaric, Isochoric, Isothermal, Adiabatic Processes & Equations

The thermodynamic process depends upon factors like temperature (T), Pressure (P), Volume (V) and heat exchanged by the system (ΔQ).

Depending on the change in these physical properties, the Thermodynamic processes are divided into different types. These types have some relations governing them.

Cyclic Process

If a system is said to be reversible, i.e., For a process if the system returns back to its initial state after doing some work then the process is said to be a cyclic process.

For the cyclic process ΔU = 0.

Now according to the First Law of Thermodynamics ΔQ = ΔW +ΔU, so if  ΔU = 0.

∴ ΔQ = ΔW

Isobaric Process

  • For a thermodynamics process if the pressure remains constant for a system, then the process is called an isobaric process.
  • So if pressure is constant the net work done by the system can be given as

W = PΔV = P(V– V1)

  • This means that the heat supplied to the system is used up partially in changing its Volume and partially in changing the temperature.

Isochoric Process

  • For a thermodynamics process, if the volume remains constant for a system, the process is known as an Isochoric process
  • For this process according to the first law of thermodynamics ΔQ = ΔW +ΔU, so if volume remains constant this means ΔV=0 hence ΔW = 0.

∴ ΔQ = ΔU

  • Hence in this process, the Heat supplied will be used to increase its internal energy

Isothermal Process

  • According to Boyle’s law for a fixed mass of gas at a constant temperature, the volume is inversely proportional to the pressure. That means that, for example, if you double the pressure, you will halve the volume. This can express this mathematically as

PV = constant.

  • As the isothermal process has a constant temperature, they are governed by Boyle’s law
  • Since temperature remains constant the internal energy of the system will also be constant, i.e., ΔU = 0.
  • Hence according to the first law of thermodynamics, the work done by the system

In this article, we are going to study the different types of thermodynamic processes.

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Similarly, the work done in isothermal process from pressure p1 & p2 is

Adiabatic Process

  • An adiabatic process is a thermodynamic process in which there is no exchange of heat between the system and surrounding, that is, the heat remains constant,

i.e. ΔQ = 0

  • For an adiabatic process, We follow Poisson’s Law,i.e.,

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  • Now according to the first law of thermodynamics ΔQ = ΔW +ΔU, so if  ΔQ = 0.
  • This means that for the adiabatic process the system performs Work (ΔW) based on the bases of internal energy since ΔW =- ΔU from the above equation
  • For the adiabatic process, the work done by the system is given as

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  • Here R is gas constant, n is molar mass and Cp and Cv are specific heat at constant pressure and volume
  • Note: The below PV graphs shows how different thermodynamic process are represented in Pressure vs Volume graph

Adiabatic Process

Fig – P-V curves for isothermal and adiabatic processes of an ideal gas

Reversible and Irreversible Process:

A reversible process is one that is performed in such a way that at the final stage of the process both the system and surroundings return to their initial state with absolutely no change. In reality, there is no reversible process.Reversible and Irreversible Process

  • If the initial and final stages for a reversible process are represented by 1 and 2. In such a process, the system will proceed from 1 to 2 at a very slow speed.
  • This is because the reversible process should not leave a trace or relic behind. A reversible process is carried out infinitely slowly with an infinitesimal gradient so that every state passed through between 1 and 2 is an equilibrium.
  • Such a process is also quasi-static in nature. Hence, it is also called the Reversible Quasistatic process.
  • These processes are hypothetical and asymptote to reality.
  • All spontaneous processes are irreversible