For millennia, humans have been fascinated with the composition of things and the workings of the chemical world. Over time we have come to understand that all matter is comprised of indivisible particles called atoms. Our understanding of how matter works has been a long pursuit. It started with figuring out how to make things burn. Humans have been fascinated with chemical reactions that burn, explode, produce loud bangs, and have brilliant colors. Early alchemists learned that throwing certain salts on a fire would produce different “magical” colors. Chinese alchemists created human kind’s first explosion with the invention of gunpowder. This chemical recipe was eventually shared across the medieval globe. Historically, humans have been fascinated with coaxing nature into doing things, like burning. This fascination, coupled with our ability to observe, record, and share, has led us to our current understanding of matter. Our understanding of chemical reactions and the equations that describe them are based on many years of trial and error. The image above is an example of this. It is a star shell bursting over the night sky. The technology of pyrotechnics, like composition of the propellant, the explosive charge, the colors, and the shapes of the burst, is a result of hundreds of years of intensive study of chemical reactions and chemical equations. We are going to study chemical reactions and chemical equations in this chapter.