A Sealed Bottle of Gases

1. Dec 5, 2013

baubletop

1. The problem statement, all variables and given/known data
A sealed bottle at 1 atm of pressure holds 1 mole of neon and 1 mole of argon gas at a temperature of 295K. The curves in the Figure (http://phlnx3.pas.rochester.edu/webwork2_files/CAPA_Graphics/Gtype43/prob01a.gif) show the distributions of velocities of the molecules of each gas.
Find the number of molecules of argon which have velocities between 250 m/s and 500 m/s.

2. Relevant equations
KE = (3/2)kT
P(v) dv $\propto$ 4πv^2 e^((-(1/2)mv^2)/kT) dv
Molar Mass of Argon = 0.03995 kg/mol

3. The attempt at a solution
Totally lost on how to set this one up. I get that I need some sort of bound on the probability of finding Argon between 250 and 500 m/s, and from there I can get an actual number, but for now I'm somewhat lost.
The graph might be giving me the answer right in front of me but I'm also having a hard time reading it (it doesn't help that it's not labeled which curve is which element...).

2. Dec 5, 2013

Staff: Mentor

Argon has a higher molar mass than neon. What does that tell you about which curve is which? As a last resort, you can count area under the curve from 250 to 500.

3. Dec 5, 2013

baubletop

It should be the top curve since vrms would be lower than Neon. I thought it would be harder than that but I just manually calculated the area and got the right answer. Guess I was overthinking it. Thanks!