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PCAT Chemical Processes – Gas Behavior
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- Oct 25, 2017
- PCAT Question of the Day
A 2 L sealed vessel contains 2 moles of nitrogen gas at 0oC. All of the following will decrease the pressure inside the vessel EXCEPT:
- nitrogen leaking out of the tank
- decreasing the temperature of the gas
- expanding the volume to 3 L
- replacing 1 mole of nitrogen gas for 1 mole of oxygen gas
Explanation
This question is testing your understanding of gas behavior according to the ideal gas law.
PV = nRT
When nitrogen leaks out of the tank, the moles of nitrogen, n, decreases. Since pressure is proportional to moles, decreasing the moles of gas will decrease the pressure making A incorrect. Since temperature is also proportional to pressure, a decrease in temperature will lower the pressure making B false. Pressure and volume are inversely related, which means that increasing the volume will result in a decrease in pressure. Therefore, C is not the correct answer, which leaves D as the correct answer. Exchanging 1 mole of nitrogen gas for 1 mole of oxygen changes the partial pressures within the system but has no effect on total pressure.
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