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MCAT Chemistry Question — Ideal Gases

If a gas occupies 0.1L at 200atm, what will its volume be at 1atm?


A. slightly less than 20L

B. 20L

C. slightly more than 20L

D. 2000L

Click for Explanation

Ideal gases undergoing pressure and volume changes are related by the expression P1V1/T1=P2V2/T2. Here, temperature is not involved and P1V1= P2V2. However, since P1 is greater than 10atm, the size of the molecules cannot be ignored and volume V1 is slightly greater than it should be for an ideal gas. Therefore, the calculated volume V2=20L is slightly larger than it should be. Choice A is correct.

A. slightly less than 20L, correct.

B. 20L, incorrect, The initial volume at a pressure of 200atm includes a small contribution from the molecules themselves, and therefore the initial volume of 0.1L is larger than the volume of an ideal gas.

C. slightly more than 20L, incorrect, See explanations for a) and b).

D. 2000L, incorrect, This answer choice incorrectly divides the initial pressure by the initial volume.

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