Boyle's Law Explained With Example Problem

Boyle's gas law states that the volume of a gas is inversely proportional to the pressure of the gas when the temperature is held constant. 
Anglo-Irish chemist Robert Boyle (1627–1691) discovered the law and for it he is considered the first modern chemist. This example problem uses Boyle's law to find the volume of gas when pressure changes.

Boyle's Law Example Problem

A balloon with a volume of 2.0 L is filled with a gas at 3 atmospheres. If the pressure is reduced to 0.5 atmospheres without a change in temperature, what would be the volume of the balloon?

Since the temperature doesn't change, Boyle's law can be used. Boyle's gas law can be expressed as:

PiVi = PfVf


Pi = initial pressure
Vi = initial volume
Pf = final pressure
Vf = final volume

To find the final volume, solve the equation for Vf:

Vf = PiVi/Pf
Vi = 2.0 L
Pi = 3 atm
Pf = 0.5 atm
Vf = (2.0 L) (3 atm) / (0.5 atm)
Vf = 6 L / 0.5 atm
Vf = 12 L

The volume of the balloon will expand to 12 L.

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