Boyle's Law states that pressure and volume are inversely proportional at constant temperature. When you compress a gas (decrease volume), its pressure increases proportionally.
P₁V₁ = P₂V₂
Initial pressure × initial volume = Final pressure × final volume
P ∝ 1/V (at constant T and n)
Common Units: atm, mmHg, torr, kPa, Pa, bar, psi
Pressure before the change
Common Units: L, mL, cm³, m³
Volume before the change
Units: Same as P₁
Pressure after the change
Units: Same as V₁
Volume after the change
Temperature (T) must remain constant
Amount of gas (n) must remain constant
No gas can enter or leave the system
P₂ = P₁V₁ / V₂
V₂ = P₁V₁ / P₂
P₁ = P₂V₂ / V₁
V₁ = P₂V₂ / P₁
P₁V₁ = P₂V₂
P₂ = P₁V₁ / V₂
P₂ = (1.50 atm)(6.00 L) / (2.00 L)
P₂ = 9.00 atm·L / 2.00 L = 4.50 atm
Answer: P₂ = 4.50 atm
✅ Makes sense: Volume decreased by 1/3, so pressure increased by 3×
Diaphragm expands lungs → volume increases → pressure drops → air rushes in
Pull plunger → volume increases → pressure drops → liquid drawn in
Squeeze balloon → volume decreases → internal pressure increases
Ascend from depth → external pressure decreases → air in lungs expands (must exhale!)
Boyle's Law ONLY works when temperature is constant. If T changes, use the Combined Gas Law instead.
P₁ and P₂ must be in the same units. V₁ and V₂ must be in the same units. Convert before calculating!
It's P₁V₁ = P₂V₂, NOT P₁V₂ = P₂V₁. Initial with initial, final with final.
If volume decreases, pressure MUST increase. If volume increases, pressure MUST decrease. Verify your answer makes physical sense!
P₁V₁ = P₂V₂ at constant temperature. Pressure and volume are inversely proportional - when one goes up, the other goes down.
Gas molecules collide with container walls. Smaller volume = more collisions per area = higher pressure. Same number of molecules, less space!
At very high pressures (molecules too close), very low temperatures (gas liquefies), or when temperature changes during compression.
Yes, as long as P₁ and P₂ use the SAME units. atm, kPa, mmHg, psi - all work! Same rule for volume units.
Boyle's Law is a special case of PV=nRT when n and T are constant. It's simpler when you only care about P and V changes.