The noble gases,listed by increasing molecular weight,are He,Ne,Ar,Kr,Xe,and Rn.If samples of 1 mole each of these gases are placed in separate containers and heated to 300 K,which gas has the greatest internal energy and the molecules of which gas have the highest rms speed?

Question

Quizplus · Accepted Answer

The internal energy of an ideal gas depends solely on its temperature, which is the same for all the gases at 300 K. Therefore, all the gases have the same internal energy. 
The rms speed of a gas molecule is given by the equation:
urms = √(3RT/M)
where R is the gas constant, T is the temperature, and M is the molar mass of the gas. 
Since the rms speed depends on the molar mass of the gas, the greatest rms speed will belong to the gas with the lowest molar mass, which is Hе. Therefore, the answer is D.

The Noble Gases,listed by Increasing Molecular Weight,are He,Ne,Ar,Kr,Xe,and Rn