Gas law問題

cellmembrane

A cylinder of compressed helium of volume 0.20 m3 is initially at a pressure of 20 atm. The
gas is used to inflate some non-elastic balloons at a pressure of 1 atm. Each balloon has a
volume of 0.10 m3. Assume that the temperature of the helium does not change.

(b) How many balloons can be inflated with this cylinder?


My calculation is: Mole of the gas initially=20 x 10^5 x 0.2 / 8.31T    where T is the temp of the gas
                            Mole of gas needed to inflate =1 x 10^5 x 0.1 /8.31T

No of balloons = Mole of the gas initially / Mole of gas needed to inflate
                       = 40

but the ans is 38.Can anyone tell me what's wrong? thank you!

cellmembrane

A vessel contains 2.4 kg of an ideal gas at 300 K. What is the mass of gas expelled from the
vessel if the temperature is raised to 400 K under constant pressure?
Thank you

cellmembrane

Find the r.m.s. speed for hydrogen at 273 K

thank you