combined gas laws?

Question

a small cylinder of helium gas used for filling balloons has a volume of 2.30 L and a pressure of 13,800 kPa at 25 degrees C. How many balloons can you fill if each one has a volume of 1.5 L and a pressure of 1.25 atm at 25 degrees C?

Answer 1

Convert the kPa to atmospheres first. 13,800 kPa = 136.2 atm. Since the temperatures are the same, it's irrelevant.

It will be easiest to figure out how much volume the cylinder gas will occupy when its pressure is dropped to 1.25 atm.

P1V1 = P2V2
V2 = P1V1/P2 = 136.2 atm*2.30L/1.25 atm = 250.6 L

250.6 L/1.5 L = 167.1, so roughly 167 balloons can be filled at that volume.