At constant temperature, pressure and volume are inversely related.

At constant temperature, pressure and volume are inversely related.

• A. They are inversely related
• B. They are directly proportional
• C. They are independent
• D. They are both constant

Answer: (A)

The key idea here is that, for a fixed amount of gas at the same temperature, pressure and volume move in opposite directions. This is Boyle’s law: P times V stays constant when temperature and the amount of gas don’t change. If you squeeze the gas into a smaller volume, the gas molecules collide with the container more often, so the pressure goes up. If you let the gas expand to a larger volume, those collisions become less frequent, and the pressure drops. So pressure is inversely related to volume under these conditions. Directly proportional would mean both increase together, which isn’t what happens. They aren’t independent, because changing one affects the other. They aren’t both constant, because changing the volume changes the pressure to keep P V constant.

The key idea here is that, for a fixed amount of gas at the same temperature, pressure and volume move in opposite directions. This is Boyle’s law: P times V stays constant when temperature and the amount of gas don’t change. If you squeeze the gas into a smaller volume, the gas molecules collide with the container more often, so the pressure goes up. If you let the gas expand to a larger volume, those collisions become less frequent, and the pressure drops. So pressure is inversely related to volume under these conditions.

Directly proportional would mean both increase together, which isn’t what happens. They aren’t independent, because changing one affects the other. They aren’t both constant, because changing the volume changes the pressure to keep P V constant.