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PCAT Chemical Processes – Ideal Gas Law

A container with a pressure of 3 atm occupies a volume of 11.2 L at 273 K. How many moles of gas are present in the container?


A) 0.5 moles
B) 1 mole
C) 1.5 moles
D) 3 moles


This question is testing your understanding of the ideal gas law, PV = nRT, and standard temperature and pressure (STP) conditions. To determine the number of moles of gas occupied under the conditions specified in this question, you must rearrange the ideal gas law to solve for n in terms of pressure, volume, temperature and the constant R.


n = PV/RT


At STP (P = 1 atm, T = 273 K), 1 mole of gas (n = 1) occupies a volume of 22.4 L. Therefore, the ratio PV/RT = n = (1)(22.4)/(0.082)(273) = 1. Since in this problem, the ratio PV/RT = n = (3)(11.2)/(0.082)(273) = 1.5, the number of moles of gas is equal to 1.5 making C the correct answer.

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