Walt suggests to Jesse that they have finished their work for now because the reaction has begun. After Jesse asks Walt how long the reaction will take, Walt explains why having a freezer would speed up the reaction: because it's exothermic.
Beakman explains what a chemical reaction is and then shows examples of three kinds of reactions which he explains are like partnerships: synthesis (marriage), decomposition (divorce), and double displacement (do-si-do).
In this Science Max Quiz, Phil explains how to differentiate chemical and physical changes. He mentions that chemical changes produce new molecules, while physical changes don't. He includes several examples of both physical and chemical changes.