In article , Don Foreman says...

PV = nkT

Your V is not the actual volume of the gas, Jim. . A 1 cu ft
container can be made to have 100 PSIA pressure at any temperature
you like.

The n above gives the number of atoms, basically.

In that equation, the V really is the actual volume. In your
example, if you have a cubic foot of a gas at 100 psia,
at say, 300K, then I can tell you how many moles of gas
there are.

Jim

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