Which law describes the inverse relationship between pressure and volume for a gas at constant temperature?

• A. Charles' Law: V/T = constant
• B. Gay-Lussac's Law: P/T = constant
• C. Avogadro's Law: V/n = constant
• D. Boyle's Law: P1V1 = P2V2

Answer: (D)

At constant temperature, the pressure and volume of a gas are linked so that their product stays the same as long as the amount of gas remains constant. This is Boyle’s law: PV = constant for a fixed amount of gas when temperature is unchanged. Intuitively, squeezing the gas into a smaller volume forces the molecules to collide with the container walls more often, which raises the pressure. Conversely, allowing the gas to expand lowers the pressure, keeping the product PV constant.

The practical implication is that if you compress the gas to half its volume, the pressure roughly doubles to maintain the same PV product, assuming ideal gas behavior. This inverse relationship is what Boyle’s law describes.

For broader context, other gas laws describe different relationships: Charles’s law shows V proportional to T at constant pressure, Gay-Lussac’s law shows P proportional to T at constant volume, and Avogadro’s law shows V proportional to the number of particles at constant T and P.