9.3 - Pressure & Volume

Pressure and volume are inversely proportional

For a fixed mass of gas kept at a constant temperature, pressure and volume are inversely proportional:

• When volume goes up, pressure goes down.
• When volume goes down, pressure goes up.

Why pressure and volume change together

• Gas pressure comes from gas particles colliding with the walls of their container.
• Reducing the volume squeezes the same particles into a smaller space. They hit the walls more frequently, so pressure increases.
• Increasing the volume spreads the particles out. They hit the walls less frequently, so pressure decreases.
• At constant temperature, the particles keep the same average speed, so only the frequency of collisions changes.