Do you think life on earth would have happened, but for chemical reactions? Exactly, it wouldn't. Take for instance, photosynthesis: the simple process of converting carbon dioxide and water to sugar and oxygen in the presence of sunlight. The diversity of plant life wouldn't have seen the light of day but for a set of reactions. To appreciate the variety in the world around us, it is critical to know the concepts, theories and laws that govern the innumerable combinations of the basic elements of nature.
Let's take chemical reactions, for a start. To truly appreciate the field, you need to get a grip on the energy transformation in a reaction, rate of reaction, and if a reaction takes place at all ‐ which depends on electronic configuration of atoms of the reactants, concentration of reactants, presence of catalysts and conditions like temperature etc. In addition, you need to know about catalysts and how they effect a reaction or impact the rate of a reaction. Once you are clear about catalysts, you will clearly appreciate how the simplest bacterium employs thousands of biological catalysts, known as enzymes, to speed up cellular reactions and thereby sustaining life.