Boyle's Law formula:
story, analogy and memory trick
The Boyle's Law formula is P₁V₁ = P₂V₂. At constant temperature, the pressure of a fixed amount of gas is inversely proportional to its volume, so P times V stays constant.
The Boyle's Law formula
- P₁, V₁initial pressure and volume
- P₂, V₂final pressure and volume
The story
Put your thumb over the tip of a syringe and pull the plunger. The volume grows and the push you feel from the air drops. Now press the plunger in: the volume shrinks and the pressure builds. When one goes up the other goes down, and their product stays the same.
Real-life analogy
Think of people in a lift. The smaller the lift (volume), the harder they press on each other and the walls (pressure).
Memory trick
Picture a seesaw with P on one end and V on the other. When one rises the other falls, and P × V stays the same.
Exam tip
It needs a constant temperature and a fixed amount of gas. The graph of P against V is a curve (a hyperbola), while P against 1/V is a straight line.
Questions about Boyle's Law
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PV = nRT
For an ideal gas, pressure times volume equals the number of moles times the gas constant times the absolute temperature.
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Molarity tells you how many moles of solute are dissolved in each litre of solution.
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pH = −log₁₀[H⁺]
pH is the negative base-10 logarithm of the hydrogen-ion concentration, so a lower pH means a more acidic solution.
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