What is the ratio of the average kinetic energies of hydrogen and helium at the same temperature?

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Kinetic energy refers to the energy of motion that matter may possess.  On the atomic scale, it refers to the motion of all the atoms in a sample of matter. The atoms may be vibrating in place, rolling around each other, or flying apart, or coming together.  In fact, even in a glass of water, should you shrink down to atomic size, you would observe water molecules exhibiting all types of motion.  If most of them are vibrating in place, you'd be observing ice; if moving around each other, water, and if expanding away from each other, steam. Each state of matter can have a measurable average kinetic energy. Most of the molecules in ice are vibrating in place, but the ice may contain some that are a bit more energetic and are rolling around -- a small amount of liquid water.  However, the average kinetic energy of all the molecules of water would be closer to ice.  The average kinetic energy, then, is exactly the same as the temperature of a system.  Whether the molecules are of hydrogen, or helium in a given system, the temperature expresses the average kinetic energy of both types of atoms within the observed system.  Therefore, whatever it is for one, it will be for the other; the ratio of one to the other, the quantity being the same, is 1.

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