Conceptual Physics (12th Edition)

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

Chapter 16 - Think and Explain - Page 317-318: 58


On average, U-238 atoms move slower than U-235 atoms in a mixture. The slower, heavier gas will diffuse more slowly through a membrane.

Work Step by Step

Being in a mixture means that gas molecules are at the same temperature. This means they have the same average translational kinetic energy per molecule. $KE = \frac{1}{2} mv^{2}$. The mass of U-238 is greater than that of U-235, so the speed v must be less to have the same average kinetic energy.
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