Energy, Force and Communication
GAS LAWS The relationship between pressure and volume in a gas
Lesson objectives
To recall that the particles that make up a gas are spread far apart from each other. To recall that these particles have random motion in all directions. Pressure in a gas is caused by the particles hitting the walls of the container holding the gas. To understand the relationship between pressure and volume in a fixed mass of gas.
Arrangement of particles in a gas
Arrangement of particles in a gas
What would happen if you heat a gas up?
Arrangement of particles in a gas
As you heat a gas up the particles would move quicker. They would hit the walls of the container with more force. This would increase the pressure in the container.
Arrangement of particles in a gas
What would happen if you reduced the volume (size) of the container?
Arrangement of particles in a gas
If the volume of the container were reduced, the particles would hit the side more often. The more often the particles hit the side the higher the pressure the gas generates.
Arrangement of particles in a gas
What would happen if you increased the size of the container?
Arrangement of particles in a gas
If the volume of the container increased – the pressure will fall, as the gas particles hit the sides less often.
Boyle’s Law
If you increase the pressure on a gas, it’s volume will fall. If you decrease the pressure on a gas, it’s volume will…..
Boyle’s Law
If you increase the pressure on a gas, it’s volume will fall. If you decrease the pressure on a gas, it’s volume will…..increase!
Boyle’s Law
Boyle’s Law
Here are some actual figures for the pressure and volume of a gas:
Pressure (Pa) Volume (cm3)
Pa is the unit of pressure in a gas and stands for Pascals
Boyle’s Law
Here are some actual figures for the pressure and volume of a gas: 100 120 150 180
Pressure (Pa) Volume (cm3)
Pa is the unit of pressure in a gas and stands for Pascals
Boyle’s Law
Here are some actual figures for the pressure and volume of a gas: 100 36 120 30 150 24 180 20
Pressure (Pa) Volume (cm3)
Pa is the unit of pressure in a gas and stands for Pascals
Boyle’s Law
Here are some actual figures for the pressure and volume of a gas: 100 36 120 30 150 24 180 20
Pressure (Pa) Volume (cm3)
Pressure x Volume (Pa cm3)
Pa is the unit of pressure in a gas and stands for Pascals
Boyle’s Law
Here are some actual figures for the pressure and volume of a gas: 100 36
3600
Pressure (Pa) Volume (cm3)
Pressure x Volume (Pa cm3)
120 30
3600
150 24
3600
180 20
3600
Pa is the unit of pressure in a gas and stands for Pascals
Boyle’s Law
These measurements show that the product (pressure x volume) is constant. This is known as Boyle’s Law after Robert Boyle who discovered the law in 1662
Pressure x Volume
or
=
constant
pV = constant
(provided the temperature and mass are constant)
So for any gas: P1 X V1 = P 2 X V2
Rearranging the equation
P1 = V1 = P2 = V2 =
P2 x V2 / V1 P2 x V2 / P1 P1 x V1 / V2 P1 x V1 / P2