A gas jar at room temperature contains a mixture of equal volumes of hydrogen with a mass of 2 and oxygen with a mass of 32. which molecules,hydrogen or oxygen, are moving faster?

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t-nez | High School Teacher | (Level 3) Associate Educator

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In a mixture of hydrogen and oxygen at the same temperature the hydrogen molecules will move faster than the oxygen molecules. 

Here's why:

Temperature is a measure of average kinetic energy. Since the two types of gas molecules are at the same temperature they have the same average kinetic energy. 

Kinetic Energy = 1/2 (mass)(velocity)^2

if 1/2 (mass of H2)(velocity of H2)^2 = 1/2 (mass of O2)(velocity of O2)^2 and the masses of H2 and O2 are 2 and 32 respectively, then:

(velocity of H2)^2 = 16(velocity of O2)^2, taking the square root of both sides we get:

velocity of H2 = 4 times the velocity of O2

This is the basis for Graham's Law of Diffusion/Effusion, which states that the ratio of speeds of two gases in inversely related to the square root of the ratio of their masses. 

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