Question

Equimolar samples of N2 and O2 are both at standard conditions (273K and 1 atm). Which sample has the higher average molecular speeds? Why?

a) N2; lighter molecules have higher average speeds
b) O2; heavier molecules have higher average speeds
c) N2; heavier molecules have higher average speeds
d) O2; lighter molecules have higher average speeds

Answer 1

The correct answer is (a) N2; lighter molecules have higher average speeds. At a given temperature, gases with lighter molar mass have higher average speeds due to the inverse proportionality of molecular speed to the square root of molar mass.

Step-by-step explanation:

The student is asking which sample (N2 or O2) has the higher average molecular speeds when under standard conditions (273K and 1 atm). The correct answer to this question is (a) N2, because lighter molecules have higher average speeds. At a given temperature, all gases have the same average kinetic energy (KEavg), but due to their lower molar mass, lighter molecules, such as N2, move faster on average than heavier molecules like O2. The molar mass of nitrogen (N2) is 28.0 g/mol, while the molar mass of oxygen (O2) is 32.0 g/mol. According to the kinetic theory of gases, the average speed of molecules is inversely proportional to the square root of their molar mass (urms ∝ 1/√M). Therefore, N2 molecules have a higher average speed than O2 molecules at the same temperature.