Chemistry: Boyle's Law

Physics: Boyle’s Law
What is Boyle’s Law?
• Boyle’s Law is one of the laws in physics that concern the behaviour of gases
• When a gas is under pressure it takes up less space:
• The higher the pressure, the smaller the volume
• Boyles Law tells us about the relationship between the volume of a gas and its
pressure at a constant temperature
• The law states that pressure is inversely proportional to the volume

Boyle’s Law formula
 Pressure is inversely proportional to the volume and can be written as:
 Pressure a 1/volume
 P=pressure in N/m2
 V=volume in dm3 (litres)
 k=constant
 This is more usually written as:
 Pressure = constant
 volume
 PV=k
 P1V1=P2V2


How we investigate Boyle’s Law
• When investigating Boyles law, a given volume of gas is sucked into a cylinder and the
end is sealed
• The temperature of the gas is kept constant
• Using several equal weights, we can apply increasing pressure to the gas
• We can calculate the pressure by dividing the force applied by the area of the top of
the cylinder
• The volume will be shown on the scale on the cylinder


Question
A deep-sea diver is working at a depth where the pressure is 3.0 atmospheres. He is
breathing out air bubbles. The volume of each air bubble is 2 cm 2. At the surface the
pressure is 1 atmosphere. What is the volume of each bubble when it reaches the surface?
How we work this out
We assume that the temperature is constant, so Boyle’s Law applies:
Formula first: P 1 x V1 = P 2 x V 2
Then numbers: = 1.0 x 2 = 3.0 x V2
Now rearrange the numbers so that you have V2 on one side, and the rest of the numbers
on the other side of the ‘equals’ symbol.