William W. answered • 03/22/20

BS in Mechanical Engineering with 35 years experience

The ideal gas law says PV=nRT. __If we assume that a gas is in a closed container where no gas is let in and none escapes__, then we can calculate how pressure, temperature, and volume change over time.

If PV = nRT, then using algebra, we can solve for nR to get nR = PV/T.

In a closed container, the number of moles of the gas will not change. And R is a constant as well. So if P_{1}, V_{1}, T_{1}, are the pressure, volume, and temperature at time 1, and P_{2}, V_{2}, and T_{2} are the pressure, volume, and temperature at time 2, then (since nR don't change P_{1}V_{1}/T_{1} = nR = P_{2}V_{2}/T_{2} or:

P_{1}V_{1}/T_{1} = P_{2}V_{2}/T_{2}

Boyle's Law says P_{1}V_{1} = P_{2}V_{2 }so, iyou can see that temperature has been removed from the equation. That's because they assume that temperature is held constant so does not play a part in this particular situation.

So, the amount of moles must be constant (the gas must be in a sealed container where nothing escapes and nothing comes in) and temperature must be constant.