Here is a site that clearly and thoroughly explains the chain rule for derivatives of composite functions. There are example problems solved, problems for the student to attempt, and answers to the student problems. Point this site out...

The ideal gas law is stated and explained at this site from the Towson University. It is then used to derive the other gas laws (Charles, Boyle's, Gay-Lussac's, Avogadro's, combined, etc.). Other gas law relationships are discussed....

An excellent site for understanding and applying the ideal gas law. The combined and other variations of the ideal gas law are derived. There are sample application problems with an abbreviated method of solving the problems.