|MadSci Network: Physics|
The underlying mechanism in the charged case would be no different from the normal case of neutral particles and walls. To see why, think for a minute about why particles bounce off of neutral surfaces to begin with. If you look very closely at a neutral atom striking a neutral surface, you'll see that the recoil comes from the electron shell of the atom repelling from the electron shells of the surface's atoms. So in fact, the pressure from the neutral case results from the electromagnetic force just as in the charged case. I mention this because, from your question, it appears you think of the pressure resulting from repulsion of like charges to be somehow different in essence from what normally occurs in a container. That said, there IS a difference between the two cases. In the charged case, the electromagnetic force between the particles and the walls is obviously larger than in the neutral case. Because it now takes much more energy for a particle to approach the walls, the effective volume of the container is decreased. The ideal gas law (PV=nkT) therefore tells us that the pressure will be greater (for the same amount of gas at the same temperature) in the charged case than in the neutral case.
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