I believe that students learn best by working and thinking through problems. I believe this is especially true for chemistry courses. Although everyone does not learn the same way, we must put in the time in order to know what does and does not work. Many students work just enough problems to familiarize themselves with a concept, but stop short of working enough problems to be truly comfortable with the actual chemistry concepts being presented. While I do believe that there is more than one way to learn something, when it comes to math and the physical sciences there is no real replacement to working your way through progressively more involved problems because they force you to think, and the process reinforces what you already know.