Which of the following gases has the highest average speed at 400K?

#A. NO_2#
#B. O_2#
#C. F_2#
#D. Cl_2#
According to my answer sheet, the correct answer is #A#, but I don't understand why. From my understanding, shouldn't the gas with the lowest molar mass have the highest speed?

1 Answer
Akaash P.
Dec 17, 2017

#B. O_2# should be the correct answer for the reasoning given.

Explanation:

Just as you stated, the gas with the lowest molar mass should have the highest speed, and #O_2# has the lowest molar mass. This relationship is true since #KE = 1/2mv^2#, so if the temperature, also known as the average kinetic energy, is constant, mass is inversely related to velocity.

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