Boyle's Law

Boyle's Law says that for a fixed amount of gas kept at the same temperature, lowering the volume makes the pressure rise, and increasing the volume makes the pressure fall. This happens because the gas molecules have the same average speed, so when they are confined to a smaller space they hit the container walls more often, creating greater pressure. The product of pressure and volume stays constant for the same sample of gas as long as temperature does not change.

Use this formula when a gas is compressed or expanded without changing its temperature, such as in syringes, pistons, scuba gear, or sealed containers. It is also useful for any problem asking how pressure or volume changes for the same gas sample at constant temperature.

• Using the formula when temperature changes, which breaks the condition for Boyle's Law
• Mixing up the variables and multiplying or dividing in the wrong place
• Forgetting to keep units consistent, such as using liters for one volume and milliliters for the other without converting