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 kinetic energy of gas molecules is directly proportional to their temperature and inversely proportional to their mass. Since the temperature is the same for both helium and oxygen molecules, the heavier oxygen molecules will have a lower average speed than the lighter helium molecules. Therefore, the helium molecules have greater average speed. Among the options given, choice D correctly identifies that the helium molecules have less mass than the oxygen molecules.

A Container Is Filled with a Mixture of Helium (Light