Question

Near sea level, the atmosphere is composed of 78% nitrogen and 20% oxygen. Other trace gases make up the remaining 2%. At room temperature, consider the following statements.
i. all the gas molecules move at the same speed.
ii. the nitrogen gas molecules, on average, move faster than oxygen molecules.
iii. the nitrogen gas molecules, on average, move faster than the oxygen molecules.
iv. some nitrogen gas molecules could move faster than some of the oxygen gas molecules.
v. some nitrogen gas molecules could move slower than some of the oxygen gas molecules.

Which of these are correct?
a. i
b. ii & iv
c. iii & iv
d. ii, iv, & v
e. all are correct

Answer 1

Answer:

the nitrogen gas molecules, on average, move faster than oxygen molecules.

some nitrogen gas molecules could move faster than some of the oxygen gas molecules.

some nitrogen gas molecules could move slower than some of the oxygen gas molecules.

Explanation:

From the kinetic theory of gases, we understand that gas molecules are in constant random motion and collide with each other as well as the walls of the container.

Molecules of in a container have the same an average kinetic energy (at the same temperature) but individual gas molecules show a distribution of kinetic energies since they have a distribution of different speeds.

This distribution of speeds stems from the fact that individual gases collide with each other in the gas phase. These collisions are elastic, consequently, the speeds of each molecule involved in the collision may change. When two molecules collide, one molecule may be deflected at a slightly higher speed and the other at a slightly lower speed, even though the average kinetic energy does remains the same.

If we compare two gases having different molar masses at the same temperature, we know that, though the gases have the same average kinetic energy, the gas having a smaller molar mass will have a higher rms speed. Therefore, the nitrogen gas molecules, on average, move faster than oxygen molecules.