# Adiabatic effusion and violation of energy conservation

## Main Question or Discussion Point

when the gas effuse out of an insulated container, its velocity is given by
$$\sqrt{\frac{2\gamma RT}{(\gamma-1)M}}$$
(irodov's problem 2.42)

This leads to the result that every mole of leaking gas has an energy of
$$\frac{\gamma RT}{(\gamma-1)}$$
whereas we know the energy contained in 1 mole of gas is
$$\frac{RT}{(\gamma-1)}$$

From where is this difference of energy coming out.

Thanks for helping!!

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Bystander
Homework Helper
Gold Member

By adiabatic, I mean no heat given to the system.
Also the process here is not in equilibrium all the time. Its a free expansion.

I am posting the exact question I am referring to (from Irodov's Problems in general physics - 2.42):

Ques: Find the rave v with which helium flows out of a thermally insulated vessel into vacuum through a small hole.
The flow rate of the gas inside the vessel is assumed to be negligible under these conditions.
The temperature of helium in the vessel is T = 1,000 K.

Ans: v = $$\sqrt{\frac{2\gamma RT}{(\gamma-1)M}}$$ = 3.3 km/s

Bystander
Homework Helper
Gold Member
What's the Joule-Thompson inversion T for He?

• mukul
it is 51 K at 1 atm

Bystander