How to Set Up Chemistry Equations

Chemical equations require that one side is balanced with the other.

Chemical equations are one way in which scientists explain with letters and numbers the molecular transformation of two or more substances that interact and undergo chemical change. This chemical change is indicated by the formation of heat, light or gas. Setting up chemical equations requires following a set of rules established and used by chemists the world over.

Things You'll Need

• Paper
• Pencil
• Chemistry textbook

Instructions

1. Write down all molecule and element symbols for the materials that will react. These are called the reactants, and they are the starting materials for any chemical reaction. Separate each molecule or element with a plus sign (+). At the end of listing all reactants, write an arrow pointing to the right, (-->). This arrow indicates that the reactants are going to react to form something new called products.

2. Write out all molecular formulas or element symbols for the products of the reaction on the right side of the arrow. Separate all products with a plus sign (+). Knowing which products will form is a skill developed over time, but there are a few ways to know immediately. You can research the products of frequently performed reactions in your textbook, seek the knowledge of a professional chemist or teacher or deduce the results for yourself from commonly known reaction behavior. For example, one such behavior is that when a metallic acid and a salt base react, the hydroxide molecule forms with the metal.

3. Check your molecular formulas to ensure that all subscripts are correct. Subscripts denote how many of each element are used in a molecule to make the molecule complete. You can confirm this through a textbook appendix or by drawing the Lewis diagrams for each molecule in uncertain cases. Specifically, make sure that all diatomic molecules (Br, I, N, Cl, H, O, F) have a subscript of 2.

4. Add molecular coefficients to molecules and elements where necessary to balance the entire equation. Molecular coefficients are multiplying factors put before a molecule in the equation to increase the number of atoms that either is needed to react or is produced by the reaction. In the end, all the elements on the reactant side of the equation (accounting for both subscripts and molecular coefficients) should be equal to the elements on the right side of the equation.

References

• Preparatory Chemistry: Chapter 4, An Introduction to Chemical Reactions