Chapter 11 · Gases
11.4Boyle's Law: Pressure and Volume
11 min · two checks
Predict
If you double the pressure on a trapped gas at constant temperature, what happens to the volume?
The idea
- Apply Boyle’s law.
- Explain the law with collisions.
Squeeze a gas into a smaller volume and the particles hit each unit of wall more often, so pressure rises. If temperature and the amount of gas are constant, pressure times volume is constant: P₁V₁ = P₂V₂. Graph volume against 1/P and you get a straight line. Graph P against V and you get a curve. Inverse does not mean “subtract.”
Units of P can be anything as long as both pressures match, and the same for volume. Solve for the unknown before you plug in numbers if that keeps the algebra calmer. A size check: if pressure went up, volume must come down. If your answer does the opposite, the variables are swapped.
Keep these
- P₁V₁ = P₂V₂ at constant T and n.
- Pressure up, volume down.
- Keep each variable’s units consistent on both sides.
Worked path
A balloon has a volume of 2.40 L at 98.0 kPa. What volume does it have at 110 kPa, same temperature?
Observe
Pressure rose, so volume should fall. T and n fixed.