OERs and Open Online Courses by Stephen Downes show different free online college courses. This would be a great tool to look at Chemistry notes, tutorials, quizzes to help clarify the material about Chemical Reactions.
MCAT study tip from The Gold Standard MCAT Prep. Complete MCAT online courses with videos and practice tests, MCAT textbook with free online access to study resources as well as tools like MP3s, MCAT flashcards and iPhone apps. http://www.mcat-prep.com/