Question

consider 2 sample of nitrogen gas. sample 1 contains 1.5 mol of N2 and has a volume of 36.7L at 25C and 1 atm. sample 2 has a volume of 16.5L at 25C and 1 atm. calculate the number of moles of N2 in sample 2

do i use the pv= nrt equation? and do i only use the information given for sample 2 since you are finding moles in sample 2?
so you can ignore the info. for sample 1?

Answer 1

You can do this two ways.
One way is to use PV = nRT and, as you say, ignore sample 1.
(1 atm)(16.7 L) = n*0.08206*298 and solve for n, number of moles.
OR you can forget the PV = nRT and use the information from the two gases. I suspect the problem is trying to illustrate Avogadro's Law that equal volumes of gases at the same P and T contain equal number of molecules.
So if 1.5 mol are in the 36.7 L sample and we want to know moles in the 16.5 L sample, we can use the ratio
1.5 mol x (16.5/36.7) = ??
You should get the same answer either way.