In PV=nRT, with temperature and volume held constant, what happens to the pressure if the amount of gas increases?

• A. Pressure increases
• B. Pressure decreases
• C. Pressure stays the same
• D. Pressure becomes zero

Answer: (A)

With temperature and volume fixed, pressure scales directly with the amount of gas. From PV = nRT, if T and V are constant, P = nRT / V, so increasing n increases P in direct proportion. Doubling the number of moles doubles the pressure because there are more particles colliding with the container walls per second. Conversely, reducing the amount of gas lowers the pressure, and if there were no gas at all (n = 0), the pressure would be zero. So increasing the gas amount results in higher pressure.