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According to Langmuir’s adsorption model for a gas on a solid surface, which statement is true?

1. The amount of gas hitting a fixed surface area is directly proportional to the gas pressure.
2. The amount of gas hitting a fixed surface area does not depend on the gas pressure.
3. The rates of adsorption and desorption of molecules from the surface are unaffected by how much of the surface is already occupied.
4. A single surface site can adsorb several molecules simultaneously.

Correct answer: The amount of gas hitting a fixed surface area is directly proportional to the gas pressure.

Solution

In Langmuir's model the rate at which gas molecules strike a fixed area of surface is directly proportional to the gas pressure. (Adsorption/desorption rates DO depend on fractional coverage, and each site holds only one molecule, so those statements are false.)

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