When the volume of a gas remains constant, what happens to pressure if temperature increases?

• A. Pressure decreases.
• B. Pressure remains the same.
• C. Pressure increases.
• D. Pressure becomes negative.

Answer: (C)

When the volume is fixed, pressure changes in direct proportion to temperature. As temperature rises, gas molecules gain kinetic energy and collide with the container walls more vigorously and more often, pushing harder on the walls. The ideal gas relation P = nRT/V shows that, with n and V constant, pressure scales with temperature, so increasing T increases P. It’s important to use Kelvin for temperature to keep the relationship linear; for example, if the temperature doubles from 300 K to 600 K while volume and the amount of gas stay the same, the pressure doubles. The other options don’t fit this behavior: heating at constant volume does not cause pressure to decrease or stay the same, and pressure doesn’t become negative in this context.