Question

7.7 mol of helium are in a 16 L cylinder. The pressure gauge on the cylinder reads 65psi. What are (a) the temperature of the gas in Celsius and (b) the average kinetic energy of a helium atom?

p=65psi=4.481592E5
p=65psi=4.42atm
n=7.7mol
v=16=.016m^3
T = PV/(nR) = (4.42*.016)/(7.7*8.31)..not working
or
(4.481592E5*.016)/(7.7*8.31)..also did not work

I was told: "You need to use SI units throughout, i.e., Pascal for pressure. And it requires absolute pressure, not gauge."
So it means i didn't use SI unit
I'm confused

Answer 1

did you try to subtract 273.15? it did want the answer in Celsius not kelvin

Answer 2

T = PV/(nR) =(4.42 * .016) / (7.7 * 8.31) = 0.0011052245
so when (0.0011052245)-(275.15)=-273.14 not working
or
(4.481592E5 * .016) / (7.7 * 8.31) = 112.062563
so when (112.062563)-(273.15)=-161.09 also did not work

Answer 3

um it looks like your having the same issue i had. try using -140 as your answer. my values were the same as yours except i had 7.6 mols and my final answer came out to 20 degrees lower than what i calculated using the same equation u used. masteringphysics go figure

Answer 4

Thanks Joe.
It worked, but don't why is that even though i used the formula( i think i used it correctly).

Answer 5

so for part b, i have to use KE=3/2kT where k=1.38*10JK^-1
so -140C becomes 133.15K

so (3/2)(1.38*10^-23)(133.15), right?

Answer 6

I meant
Thanks Joe.
It worked, but don't know why is that even though i used the formula( i think i used it correctly).

Answer 7

perhaps wrong gas constant unit. .08206

Answer 8

almost perfect using the pascals for pressue, but you need to put in into Celcius. the T in PV=nRT is in kelvins... so minus 273 from your original answer with the pascal units of pressure.

Answer 9

nevermind im having the same issues. this program is worse than HIV

Answer 10

apparently you need to use absolute psi which is 14.7+gauge pressure.... then convert that into pascals and use PV=nRT...