His law gives the relationship between pressure and volume if temperature and amount are held constant.
If the volume of a container is increased, the pressure decreases.
If the volume of a container is decreased, the pressure increases.
Why?
Suppose the volume is increased. This means gas molecules have farther to go and they will impact the container walls less often per unit time. This means the gas pressure will be less because there are less molecule impacts per unit time.
If the volume is decreased, the gas molecules have a shorter distance to go, thus striking the walls more often per unit time. This results in pressure being increased because there are more molecule impacts per unit time.
The mathematical form of Boyle's Law is: PV = k
This means that the pressure-volume product will always be the same value if the temperature and amount remain constant. This relationship was what Boyle discovered.
This is an inverse mathematical relationship. As one quantity goes up in the value, the other goes down.
In the ChemTeam classroom, a student occasionally asked "What is the value for k?"
Suppose P1 and V1 are a pressure-volume pair of data at the start of an experiment. In other words, some container of gas is created and the volume and pressure of that container is measured. Keep in mind that the amount of gas and the temperature DOES NOT CHANGE. The ChemTeam does not care what the exact numbers are, just that there are two numbers. When you multiply P and V together, you get a number that is called k. We don't care what the exact value is.