It isn't impossible to double the volume of a given number of moles of gas! Imagine two 1 L bottles with a stopper between them. One bottle is evacuated (let's say there is nothing in there), and the other, which is the same volume, has 1 mole of gas in it. The stopper now pops, and the gas has twice the volume to fill. Now there is 1/2 mole in each bottle, the same number of moles total, and since the volume has doubled the pressure is half what it was before. This is an application of Boyle's law, a portion of the ideal gas law.
 |
Pressure is inversely proportional to the volume |
