# Thermodynamics Pressure Calculation

A spherical balloon is filled with helium atoms (Note: 1 atm = 101.3 kPa).
What is the total translational KE of the atoms if the balloon has a diameter 26.0 cm at 46.0 °C and the pressure inside the balloon is 121.6 kPa?

The answer is 1680J but I can't get it.

I used KE=3/2kT (in J/molecule) and then multiplied that number by the number of molecules PV=nRT. Am I working it out wrong or using the wrong numbers (like should I use Kelvin for temperatures)?

KE=3/2*1.38x10^-23*46 =2.4x10^21
n=PV/RT = (121.6*9.2x10^-3)/(8.314*(46+273)) Not sure if I should use Kelvin here
n= 4.22x10^-4
KE*n = 2.4x10^21* 4.22x10^-4=1x10^18J (which is so off the right answer).

Oops. Somehow my thread got posted twice...!?! Sorry...
I dunno how to delete...

never mind. I got it. Thanks for looking anyway.

Borek
Mentor
Oops. Somehow my thread got posted twice...!?! Sorry...
I dunno how to delete...
Click on Edit button, look for Delete button.

Note that Edit is active only for a limited period of time, if you will wait for too long, posts is no longer editable.