Chemical reactions [take a quiz on this topic]

Chapter Two: The Chemistry of Biology Elements and atoms Molecules and their formation Molecular and structural formulas Chemical reactions Acids, bases, and buffers Organic compounds and the importance of carbon Different types of organic compounds Enzymes and coenzymes Factors which affect the efficiency of an enzyme Diffusion

A chemical reaction is simply the breaking of bonds and/or the formation of new bonds between atoms and molecules. Chemical reactions are written in a very simple way; they look somewhat like a math equation. On the left side are the compounds (compounds are just collections of the same type of molecule) that existed before the reaction, and on the right side are the compounds which formed after the reaction. These compounds are called the reactants and the products respectively. Below is a simple chemical reaction that often occurs within cells.

C₆H₁₂O₆ + 6O₂ 6CO₂ + 6H₂O + energy

Now, let's look at this reaction in further detail. The reactants in this reaction are C₆H₁₂O₆ (also known as glucose, a type of sugar) and O₂ (the form of oxygen one would find in the atmosphere). Notice that one molecule of glucose and six molecules of O₂ are required for the reaction. The products of the reaction are CO₂ (carbon dioxide) and H₂O (water), six molecules of each. Also produced is energy, which is released when some of the bonds in the glucose molecule are broken.

Try counting how many atoms of carbon, oxygen, and hydrogen there are on either side of the reaction. You'll find that there are 6 carbon atoms, 18 oxygen atoms, and 12 hydrogen atoms on both sides. In all chemical reactions in a cell, the number of atoms of each element on either side of the reaction is equal.