Revision Notes for Chemical Science: Joule - Thomson Effect! (Download PDF)

By Renuka Miglani|Updated : December 28th, 2021

Hello Aspirants,

Are you looking for some short and reliable notes during your CSIR-NET preparations? Then, you have come to a perfect place!

Candidates preparing for their CSIR NET exam might need to get some short study notes and strategies to apply while preparing for the key exam of their life. At this point, We at Byjus Exam Prep come up with short notes on the Joule – Thomson Effectwhich comes under the Physical Chemistry section of the Chemical Science syllabus. 

Our experienced subject matter experts have meticulously designed this set of short notes on the Joule – Thomson Effect to give you the most standard set of study materials to be focused upon. In this cut-throat competitive world, students need to prepare themselves with the best study materials to help them learn and for their future. So, here we are offering the best study notes that are reliable and can be used by the students during their preparations for the upcoming CSIR-NET 2022 exam.

Joule – Thomson Effect (Download PDF)

Porous Plug Experiment: When any gas is subjected from a region of higher pressure to a lower pressure through a porous plug adiabatically, cooling takes place except for H, and He. At the same conditions of temperature and pressure when these gases are subjected from a higher-pressure region to a lower-pressure region through a porous plug adiabatically, heating takes place.

This effect is known as the Joule-Thomson effect'. It is an isenthalpic and adiabatic process.


As Joule – Thomson effects is an adiabatic Process, therefore,

dQ = dU + dW

  0 = dU + dW

-dW = dU …(1)                      ('. dQ = 0)

From the above expression, it can be said that the work done by the gas is equal to the change in internal energy.

– PdV = dU

– P(V2 – V1) = U2 – U1

– PV2 + PV1 = U2 – U1

U1 + PV1 = U2 + PU2

H1 = H2

H2 – H1 = 0


H = constant

So, Joule – Thomson effect is an isenthalpic process.

Joule Thomson Coefficient:

H = H (T, P)




Joule – Thomson Coefficient and Ideal gas equation of state:

The expression of Joule-Thomson coefficient can be expressed as:





Inversion temperature (Ti):

The temperature at which the value of becomes zero which means neither heating nor cooling takes place and gas behaves ideally is called inversion temperature.




Joule-Thomson Coefficient for a Real Gas:

Joule-Thomson coefficient may be positive or negative or zero depending upon the temperature and pressure of the gas. Since the change in pressure, dp, in Joule-Thomson experiment is always negative, it follows that dT will be negative when is positive, and vice-versa.





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