Both hydrogen sulfide (H2S) and ammonia (NH3) have strong, unpleasant odors. Which gas has the higher effusion rate? If you opened a container of each gas in a corner of a large room, which odor would you detect first on the other side of the room? Assume the temperature is constant. Explain your answer.

Question

Jazlyn Wolf

Chemistry

17 August, 11:43

Both hydrogen sulfide (H2S) and ammonia (NH3) have strong, unpleasant odors. Which gas has the higher effusion rate? If you opened a container of each gas in a corner of a large room, which odor would you detect first on the other side of the room? Assume the temperature is constant. Explain your answer.

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Efrain Rojas · Answer 1

The Law of Graham or efussion law of gases states the the rate of efussion is inversely related to the square root of the molar mass of the gas.

This is, naming MM the molar mass:

rate of efussion α 1 / (√ (MM)

So you can relate the rate of efussion of two gases as:

rate a / rate b = √ (MM of b) / √ (MM of a)

So to answer the question you just need to calculate the MMs of the two gases:

H2S: 2*1g/mol + 32 g/mol = 34 g/mol

NH3: 14 g/mol + 3*1g/mol = 17 g/mol

=> √34/√17 = √2

=> Rate NH3 / Rate H2S = √2 = > Rate NH3 > Rate H2S

There you have the demonstration and explanation of the situation.

NH3 has higher effussion rate than H2S because it is lighter (lower molar mass).

Same proportion is valid for the diffusion of the gases, which is the term related with the movement of a gas through other gases (air in this case), so you will detect first the odor of NH3, because its diffusion rate is higher than that of the H2S.