The molecules of which gas have highest speed?
Correct answer: A. H2 at -73oC
- A. H2 at -73oC
- B. CH4 at 300 K
- C. N2 at 1,027oC
- D. O2 at 0oC
Explanation
For gas molecules at comparable conditions, average speed is proportional to the square root of T/M, where T is in kelvin and M is molar mass in g/mol. The values of T/M are H2: 200 K ÷ 2 g/mol = 100 K mol/g, CH4: 300 K ÷ 16 g/mol = 18.75 K mol/g, N2: 1300 K ÷ 28 g/mol = 46.4 K mol/g, and O2: 273 K ÷ 32 g/mol = 8.5 K mol/g, so H2 has the greatest speed and option a is correct. Students may select c because nitrogen has the highest temperature, overlooking the effect of molar mass and the fact that -73°C equals about 200 K.
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About Kinetic Molecular Theory
Kinetic molecular theory explains gases as rapidly moving particles separated by large distances, with negligible volume and negligible intermolecular attraction in the ideal model. It relates temperature to average kinetic energy and explains gas pressure, Boyle's and Charles's laws, diffusion, effusion and the conditions under which real gases deviate from ideal behavior.
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