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Thermodynamic Processes


There are some general process through which a thermodynamic systems can interact with another system. The process is listed below:
  • Quasi Static process
  • Isothermal process
  • Adiabatic process
  • Isochoric process
  • Isobaric process
  • Cyclic process

Quasi-Static Processes (means nearly static or nearly equilibrium)


Suppose a system interacts with some other system in a process which is carried out so slowly that the system remains arbitrarily close to equilibrium at all stages of process. Such a process is said to be Quasi-Static for the system.

Isothermal Process


If the change in pressure and volume of a gaseous system be brought about in such a manner that its temperature remains the same throughout, it is called as an isothermal process. Such a process can only be brought about when the system under study is in good thermal contact with the surroundings.

Thus in an isothermal process, heat must be quickly conducted from the gas to the surrounding or vice versa, and this can be possible only when the containing vessel is a perfect conductor of heat.

An ideal isothermal process must be infinitely slow and must consist of infinitely small steps, in perfect thermal communication with the surroundings.

The ideal gas equation for the isothermal process is,
P V = Constant

Work Done during Isothermal Process
Let one gram of perfect gas be allowed to expand very gradually under isothermal conditions. Let its initial volume and pressure be (V1, P1) and the final volume and pressure be (V2, P2) so that its temperature remains at T.

By considering a small increase ∆V in the volume of the gas at pressure P, the work done by the gas is,
∆W = P ∆V
(or)
dW = P dV
 
Total work done by the gas during the whole expansion from volume V1 to Volume V2 can be obtained as,



 
In isothermal process, the temperature remaining constant, the internal energy of the gas undergoes no change. The whole of the heat supplied to the gas is thus converted into external work done by the system.
###SUB-TOPIC###Adiabatic process###
The word adiabatic literally means "heat not passing through". An adiabatic process is one in which heat is neither allowed to enter nor leave the system under study.

It is thus a process which takes place in complete thermal isolation from the surroundings. So an obvious requirement for such a process therefore is that the system should be enclosed in a perfect insulator of heat.

The ideal gas equation for an adiabatic process is
PVγ = Constant

where γ is known as the ratio of the specific heats at constant pressure and at constant volume.


Work Done during Adiabatic Process
Let one gram of perfect gas be allowed to expand very gradually under isothermal conditions. Let its initial volume and pressure be (V1, P1) and the final volume and pressure be (V2, P2).

Thus if an ideal gas undergoes a change in its state adiabatically from (V1, P1) to (V2, P2), then
P1V1γ = P2V2γ
Total work done by the gas is,





As stated earlier in an adiabatic process, no heat is allowed to enter or leave the system, the external work W is done by the gas at the expense of its own internal energy.
 

Isochoric Process


If the volume of the system be kept constant and its pressure and temperature changed, the process is called an isochoric process.

Here we are going to maintain constant volume so that the work done will be zero.
 
 
The whole heat supplied is used to increase the internal energy of the system.

Isobaric Process


If the pressure of the system be kept constant and its volume and temperature changed, the process is called an isochoric process. The heat absorbed goes partly to increase internal energy and partly to do work. The change in temperature for a given amount of heat is determined by the specific heat of the gas at constant pressure.

Work done by the gas

W = P (V2 - V1) = µR (T2 - T1)

Cyclic Process


The cyclic process is where the gaseous system is subjected to a series of changes of pressure and volume, such that the system returns to its initial state.

For a cyclic process ∆U = 0. So the total amount of heat supplied to the system is equal to the work done by the system.

Type of Processes

Constraint Quantity

Isothermal

Temperature constant

Isochoric

Volume constant

Isobaric

Pressure constant

Adiabatic

Heat is neither allowed to enter nor leave the system





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