Question

Arrange the following gases in order of increasing average molecular speed at 25 degrees Celsius. He, O2, CO2, N2

A. He < O2 < N2 < CO2
B. CO2 < He < N2 < O2
C. He < N2 < O2 < CO2
D. CO2 < N2 < O2 < He
E. CO2 < O2 < N2 < He

Answer 1

At a given temperature, gases composed of lighter molecules have higher average molecular speeds, while gases consisting of heavier molecules have lower average molecular speeds. The correct answer is option D. CO2 < N2 < O2 < He.

Step-by-step explanation:

At a given temperature, all gases have the same average molecular speed (Urms) for their molecules. Gases composed of lighter molecules have more high-speed particles and a higher Urms, with a speed distribution that peaks at relatively higher speeds. Gases consisting of heavier molecules have more low-speed particles, a lower Urms, and a speed distribution that peaks at relatively lower speeds.

In this case, He (helium) has the lowest molecular weight, so it will have the highest average molecular speed. The next gas is N2 (nitrogen) followed by O2 (oxygen), and finally, CO2 (carbon dioxide) will have the slowest average molecular speed because it has the heaviest molecular weight.

Therefore, the correct answer is option D. CO2 < N2 < O2 < He.