Are the variables in the combined gas law directly related?

Yes it is directly proportional

Explanation:

Well a chemical change is when substances are combined and the final product is permanent

For example ... baking a cake is a chemical change because the ingredients in the cake can't be separated as separate substances like they were in the beginning

A physical change is where the substances isn't changes, but just the appearance.

For example... origami or cutting paper is considered a physical change because even though it was cut or folded it is still paper.  

One similarity is that the physical and chemical changes are categorized under characteristic changes

-+ Hope I helped +-