Thermodynamics: Ideal Gas Law, find the temperature

[AbbeyC172]

Homework Statement

A 3-ft^3 container is filled with 2-lbm of oxygen at a pressure of 80 psia. What is the temperature of the oxygen?

Homework Equations

pV= nRT
T= PV/nR
R= 10.7316 psia x ft^3/ lbmol x R

The Attempt at a Solution

Hi everyone! So I understand how to use the Ideal Gas Law but my answer doesn't seem right so I think I might have messed up a conversion somewhere?

T= ?
V= 3 ft^3
n= 2 lbsm
R= 10.7316 psia x ft^3/ lbmol x R
P= 80 psia

Using T= PV/nR

T= (80 psia)(3 ft^3)/(2 lbsm)(10.7316 psia x ft^3/ lbmol x R)

I was able to cancel out the psia, ft^3, lbmoles, and was left with R which I am assuming means my temperature in Rankine? After calculating the above I got:

T= 240/21.46= 11.18 R

Can anyone let me know if I did this correctly? Thank you so much in advance.

 

[Chestermiller]

n is not 2 lbs. How many lbs are there in a lb mole?

 

[AbbeyC172]

Thank you for reply! Lbs of what? All I found was a lb mole is 12 lbs of 12C. I’m not going to lie. Moles confuse the heck out of me.

 

[Chestermiller]

Thank you for reply! Lbs of what? All I found was a lb mole is 12 lbs of 12C. I’m not going to lie. Moles confuse the heck out of me.

A lb mole of oxygen has a mass of 32 lbm. (i.e., equal to its molecular weight of oxygen). So, you have 1/16 of a lb mole. Your answer is off by a factor of 32.

 

[AbbeyC172]

A lb mole of oxygen has a mass of 32 lbm. (i.e., equal to its molecular weight of oxygen). So, you have 1/16 of a lb mole. Your answer is off by a factor of 32.

Ah I get it now! So could I just put in 0.0625 in instead of the 2lbm?

 

[Chestermiller]

Ah I get it now! So could I just put in 0.0625 in instead of the 2lbm?

0.0625 is the number of lb moles represented by 2 lbm.