Great questions! Heat or energy, in one form or another, is absolutely essential in making a chemical reaction work. We can generally think of a chemical reaction happening because of two factors: energy and “randomness.” The first part is simple to understand: if the chemical reaction requires an energy input (endothermic), then the more energy, such as heat, you put in the stronger the drive for the reaction. However, if the reaction gives away energy (exothermic), then it’d be best to try and extract as much heat as possible to keep the reaction running. The second component is a little more difficult to understand. You can think of “randomness” as the order in a particular situation. Generally chemical reactions, and the universe, tend to want to be disordered. Think about this as cleaning your room: it just sometimes feels like your room becomes cluttered naturally and you have to work to clean it! If a chemical reaction results in more order in the end, you will need to put in extra energy to do this. Heat plays an important role in, for example, the combination of two molecules into one bigger one. This is because the two molecules should be aligned correctly for the reaction to happen. The more heat there is, the faster they jiggle around and the better chance they have of finding their right position to react.