Question

A cylinder with a movable piston contains 2.00 g of helium, He, at room temperature. More helium was added to the cylinder and the volume was adjusted so that the gas pressure remained the same. How many grams of helium were added to the cylinder if the volume was changed from 2.00 L to 2.526 L ? (The temperature was held constant.)

Enter your answer in units of grams.

Please show all work

Answer 1

moles of Helium= mass/ molar mass , molar mas of helium= 4 g/mole

initial moles of helium, n1= 2/4=0.5

from gas law, PV= nRT

pressure amd temperature when kept constant

V/n= constant

or V1/n1= V2/n2

given V1= 2L and V2= 2.526 L , n2= final moles of gas

n2= V2*n1/V1=0.5*2.526/2=0.6215 moles

but this includes 0.5 moles added at the begining

hence moles of heium to be added additionally= 0.6215-0.5=0.1215

mass of helium to be added= moles* molar mass =0.1215*4=0.4860 gm