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 V= 4/3*pi *radius^3 =4/3*pi*(13/100)^3 =9.2*10^-3 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).