Reactants and Products: Reading Chemical Equations

You create a new substance with chemical reactions. The chemical substances that are eventually changed are called the reactants, and the new substances that are formed are called the products. Chemical equations show the reactants and products, as well as other factors such as energy changes, catalysts, and so on. With these equations, you use an arrow to indicate that a chemical reaction has taken place. Beneath or above this arrow people sometimes indicate that a specific catalyst is used, or acidic conditions or heat is applied, and so on. In general terms, a chemical reaction follows this format:

Reactants → Products

For example, take a look at the reaction that occurs when you light your natural gas range in order to fry your breakfast eggs. Methane (natural gas) reacts with the oxygen in the atmosphere to produce carbon dioxide and water vapor.

(If your burner isn’t properly adjusted to give that nice blue flame, you may also get a significant amount of carbon monoxide along with carbon dioxide.) You write the chemical equation that represents this reaction like this:

You can read the equation like this: One molecule of methane gas, CH₄(g), reacts with two molecules of oxygen gas, O₂(g), to form one molecule of carbon dioxide gas, CO₂(g), and two molecules of water vapor, H₂O(g). The 2 in front of the oxygen gas and the 2 in front of the water vapor are called the reaction coefficients. They indicate the number of each chemical species that reacts or is formed.

Methane and oxygen are the reactants, and carbon dioxide and water are the products. All the reactants and products are gases (indicated by the  ’s in parentheses). In this reaction, all reactants and products are invisible, but you do feel another product of the reaction: heat. The heat being evolved is the clue that tells you a reaction is taking place.