A gas is sealed in a bottle at 25°C and 1.50 atm pressure. How must the storage conditions be changed to bring the gas to Standard Temperature and Pressure (STP) ?

We first assume that the gas is an ideal gas so we can use the relation PV = nRT where P is the pressure, V is the volume, n is the number of moles R is the gas constant and T is the temperature. In a closed system, the number of moles should be constant since mass cannot be created or destroyed. So the only thing we can manipulate here is the volume of the system. We do as follows:

PV/T = nR = k

P1V1/T1 = P2V2/T2

V2 = P1V1T2/T1P2

V2 = 1.50 (298.15) V1 / (273.15) (1.0)

V2 = 1.64V1

Therefore, the volume should be changed by a factor of 1.64 of the original volume.