College Chemistry : Solutions, States of Matter, and Thermochemistry
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Example Questions
Example Question #21 : Gases
Suppose that gas A effuses at a rate that is twice that of gas B. If the mass of gas A is halved and the mass of gas B is doubled, which of the following correctly describes the new relative effusion rates of these two gasses?
Gas B will now effuse at a rate 
Gas A will now effuse at a rate 
Gas B will now effuse at a rate 
Gas A will now effuse at a rate 
Gas A will now effuse at a rate
For this question, we're given the relative effusion rates for two gasses. We're then told how the mass of each of these gasses is changed, and then we're asked to determine the new relative effusion rates of the two gasses.
First, we can recall the expression that describes the dependence of the effusion rates of two gasses on their mass. Since we're told that the rate of gas A is twice that of gas B, we can write the following expression.
Furthermore, since we're told that the mass of gas B is doubled and the mass of gas A is halved, we can determine how the rate will change.
Thus, we can see that the rate will change by a factor of two. Hence, the new rate will be 
Example Question #1 : Effusion
A sample of Ne(g) effusses through a tiny hole in 60.7 s. An unknown gas, under identical conditions, effusses in 45.6 s.
What is the molar mass of the unknown gas?
To solve this problem use Graham's Law of Effusion
By plugging in the values we can rewrite the equation as
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