Isothermal Process

Isothermal Process

When a thermodynamics system undergoes a physical change in such a way that its temperature remains constant, then the change is known as isothermal changes.

What is Isothermal Process?

When a gas undergoes expansion or compression at constant temperature, the process is called isothermal process. This process is basically a thermodynamic process. Usually there are two phenomena under which this process can take place.

If a system is in contact with a thermal reservoir from outside, then, to maintain thermal equilibrium, the system slowly adjusts itself with the temperature of the reservoir through heat exchange. In contrast, in another phenomenon, the system doesn’t change its temperature. This is known as Adiabatic Process.

Let us consider a gas in a cylinder provided with a frictionless piston. The cylinder and the piston are made up of conducting material. If the piston is pushed down slowly, the heat energy produced will be quickly transmitted to the surroundings. Hence, the temperature remains constant but the pressure of the gas increases and its volume decreases.

The equation for an isothermal process is PV = constant.

Isothermal Process Example: This process can occur in any kind of object, system or living cells. Changes of state or phase changes of different liquids through process of melting and evaporation, are also isothermal process.

For an ideal gas, the product of pressure and volume (PV) is a constant if the gas is kept at isothermal conditions that is a constant pressure and temperature. Ideal gas literally means a hypothetical gas whose molecules don’t interact and faces an elastic collision with each other.

Isothermal Process Formula: A process in which the temperature remains constant is called an isothermal process. From the starting of the process till the end, the temperature remains constant.

For the process we have the equation as:

PV = Constant

If a system undergoes changes from the state A to B, considering an isothermal process, the temperature remains constant, i.e., in isothermal surface then,

P₁V₁ = P₂V₂ = nRT


n = Number of moles present in the gas

R = Ideal Gas Constant

T = Constant for Isothermal Process.