Inversion Temperature

It is the temperature at which gas shows neither cooling effect nor heating effect i.e., Joule-Thomson coefficient µ = 1. Below this temperature, it shows cooling effect and above this temperature, it shows heating effect.

Any gas like H2, H­e etc, whose inversion temperature is low would show heating effect at room temperature. However, if these gases are just cooled below inversion temperature and then subjected to Joule-Thomson effect, they will also undergo cooling.

Trips & Tricks

1. If the number of molecules present in 1 c.c. of the gas or vapour at S.T.P., then that is called loschmidt number. Its value is 2.687 ´ 1019 per c.c.

2. CO2 > SO2 > SO3 > PCl3 is order of rate of diffusion.

3. Vapour density is independent of temperature and has no unit while  absolute density is dependent of temperature and has unit of gm–1

4. The isotherms of CO2 were first studied by Andrews.

5. 1 Cal = 4.2 Joule, 1 Kcal = 4200 Joule

6. The gas which has least mean free path has maximum value of a, is easily liquefied and  has maximum value of Tb.

7.  Tc < Tb < Ti

8. For critical constants, compression factor Z is < 1.

9. Boyle’s law and Avogadro’s law are applicable under limiting condition.   This limiting condition is P ® 0.

10. Tc = 0.296 Tb ; Ti = 6.75 Tc

11. Mean free path increases if H2 is replaced by He.

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