Molecular speeds: A container is filled with a mixture of helium (light molecules) and oxygen (heavy molecules) gases. A thermometer in the container reads 22°C. Which gas molecules have the greater average speed?
A) It is the same for both of the gases because the temperatures are the same.
B) The oxygen molecules do because they are diatomic.
C) The oxygen molecules do because they are more massive.
D) The helium molecules do because they are less massive.
E) The helium molecules do because they are monatomic.

Question

Quizplus · Accepted Answer

The average speed of gas molecules is directly proportional to their molecular mass. Since helium molecules are less massive than oxygen molecules, they have a greater average speed at the same temperature. The fact that helium molecules are monatomic also contributes to their greater average speed compared to diatomic oxygen molecules.

Molecular Speeds: a Container Is Filled with a Mixture of Helium