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Jimmy Snyder
Feb25-12, 04:10 PM
P: 2,179
Also, make note of this from the link:

Quote Quote by J.C Maxwell
One of the best established facts in thermodynamics is that it is impossible in a system enclosed in an envelope which permits neither change of volume nor passage of heat, and in which both the temperature and the pressure are everywhere the same, to produce any inequality of temperature or of pressure without the expenditure of work.
For the purpose of this discussion, heat is the same thing as energy, i.e. the envelope should permit no passage of energy. The examples you have given us all depend on gravity to provide the energy for the heated gas to rise. This energy is in the form of a potential gradient which comes from outside the container.