If a gas expands against vacuum what is the work done on it
Answers
The point is,in a vacuum,there is nothing that the gas can do work on!
Also,there is nothing that the gas has to overcome its pressure to expand,so the work it does in expanding is zero.
For another thing,pressure of a gas is the force that its particles exert on the walls of their container divided by the area.But in a vacuum there is no container,so the pressure is zero.
For another reasoning leading to pressure being zero.In a vacuum,whatever the temperature of the gas is,its higher than the temperature of the environment,so it radiates energy until its temperature reaches 0K(classically). And using
P
V
=
n
R
T
PV=nRT
,we will have
P
V
=
0
PV=0
. But the volume of the gas can't be zero,so P=0. Using the ideal gas equation is justified because in a vacuum,the only force on the particles is the force by other ones. There is also diffusion to the directions leading to outside of the gas because the concentration decreases in those directions and I think the diffusion flux is dominant so the gas expands and it will behave like an ideal gas with a very good approximation.
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