This document discusses chemical reactions and the key concepts surrounding them. It defines a chemical reaction as a process where substances are transformed into different substances. It explains that reactants are written on the left side of a chemical equation, and products are written on the right side. There are several types of chemical reactions including combination, decomposition, displacement, oxidation and reduction reactions. The speed of chemical reactions can be affected by various factors like particle size, temperature, concentration and the presence of catalysts. Chemical reactions can be exothermic, releasing heat, or endothermic, absorbing heat.