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At what temperature will O2 molecules have the same mean kinetic energy as H2 molecules at -73 deg C?

1. 127 deg C
2. 257 deg C
3. -73 deg C
4. -173 deg C

Correct answer: -73 deg C

Solution

The mean kinetic energy per molecule of an ideal gas is (3/2)k_B T, where T is the absolute temperature. This is independent of the molecular mass. Therefore, O2 molecules have the same mean kinetic energy as H2 molecules at the same temperature: -73 deg C.

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