Conceptual Physics (12th Edition)

Published by Addison-Wesley
ISBN 10: 0321909100
ISBN 13: 978-0-32190-910-7

Part 3 - Multiple-Choice Practice Exam: 11

Answer

The fastest molecules are those of hydrogen.

Work Step by Step

On average, hydrogen molecules move faster than oxygen and nitrogen molecules at the same temperature. Having the same temperature means the gases have the same average translational kinetic energy per molecule. $KE = \frac{1}{2} mv^{2}$. The mass m of a hydrogen molecule is much less than that of an oxygen or a nitrogen molecule, so the speed v must be greater to have the same average kinetic energy.
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