A gas occupies a volume of 72 ml at 400 k and 800 torr. if the temperature drops to 200 k and the pressure changes to 400 torr, what volume would the gas occupy?

We are tasked to solve for the volume of the gas that occupies when pressure and temperature changes to 400 Torr and 200 Kelvin from Torr and 400 Kelvin. We can use ideal gas law assuming constant gas composition and close system. The solution is shown below:

P1V1 / T1 = P2V2 / T2

V2 = P1V1T2 / T1P2

V2 = 800*72*200 / 400*400

V2 = 72 ml

The answer for the volume is 72 ml.