Holding volume and temperature constant, if the amount of gas (in moles) is doubled, what happens to the pressure?

• A. Pressure halves
• B. Pressure remains the same
• C. Pressure doubles
• D. Pressure quadruples

Answer: (C)

Holding volume and temperature fixed, pressure scales with the number of gas particles. From PV = nRT, rearranging gives P = nRT / V. Since R, T, and V are constants, P is directly proportional to n. Doubling the amount of gas doubles the numerator, so the pressure doubles. More particles mean more collisions with the container walls per unit time, raising the pressure in a linear fashion.