Effusion and Diffusion
Effusion
Effusion is the escape of gas through a small hole into an evacuated container. Because larger molecules are more cumbersome, and more difficult to fit through a small orifice, the rate of effusion is slower for larger molecules. Consequently, the rate of effusion of a gas is inversely proportional to the square root of its mass, or
When comparing two gases, since effusion involves the relative movements of two gases, it can only be measured subjectively as a ratio rather than objectively.
Thus, the k's cancel, and the result is:
Thus, the k's cancel, and the result is:
where M1 and M2 are the molar masses of the gases. This is called Graham's Law of Effusion
Diffusion
Diffusion describes the mixing of gases, usually to mark the spread of one gas from an area of higher concentration to an area of lower concentration.
Diffusion is calculated as a ratio of the Root Mean Square Velocities of two molecules. Because the equation is a ratio, all the constants cancel out. Assuming constant temperature, the only factor affecting diffusion rate is molar mass. Smaller molecules tend to diffuse faster than larger molecules by virtue of their smaller mass, in the same way that a lean athlete can run faster than an overweight couch potato. For this reason, diffusion is calculated in much the same way as effusion.
Diffusion is calculated as a ratio of the Root Mean Square Velocities of two molecules. Because the equation is a ratio, all the constants cancel out. Assuming constant temperature, the only factor affecting diffusion rate is molar mass. Smaller molecules tend to diffuse faster than larger molecules by virtue of their smaller mass, in the same way that a lean athlete can run faster than an overweight couch potato. For this reason, diffusion is calculated in much the same way as effusion.
Practice Problems
1. What is the ratio of the effusion between 20.0 grams of Oxygen Gas and 10.0 grams of Hydrogen gas?
2. Chlorine gas and nitrogen gas were added to a sealed linear container with 2 compartments. Nitrogen gas is released from the left chamber and Chlorine gas is simultaneously released from the right. Which gas will reach the center of the container first? Show mathematically.
3.If Carbon Dioxide were to race Compound X which has a molecular mass of 44 grams/mole, who would win?
4. Element X and Element Y are always tied in a race of effusion; however, element X goes through multiple decays. Who will win if a race were to occur?
2. Chlorine gas and nitrogen gas were added to a sealed linear container with 2 compartments. Nitrogen gas is released from the left chamber and Chlorine gas is simultaneously released from the right. Which gas will reach the center of the container first? Show mathematically.
3.If Carbon Dioxide were to race Compound X which has a molecular mass of 44 grams/mole, who would win?
4. Element X and Element Y are always tied in a race of effusion; however, element X goes through multiple decays. Who will win if a race were to occur?