What Is a Word Equation in Chemistry?

Word Equations

• When two or more elements interact with one another, a chemical reaction may occur. For example, when iron and oxygen interact, rust -- iron oxide -- forms. Simply explaining the process does not reveal much about what is happening on a molecular level. Word equations describe a chemical reaction. The equation shows the elements present, includes the number of molecules in each element and may provide the state of each substance (such as solid, liquid, gas or aqueous).

Parts of an Equation

• Word equations have two parts: the reactants and the products. The reactants are the elements that begin the chemical reaction. The product is the result of the chemical reaction. Word equations use plus signs to separate each element or compound and an arrow to indicate the difference between the reactants and the products. Numbers to the left of an element or compound indicate the number of molecules present. Parentheses to the right of an element or compound indicate that state of the substance.

Example

• Water forms when hydrogen gas burns in the presence of oxygen. A simple word equation for this chemical reaction could be: hydrogen plus oxygen equals water. You may also write it out in symbols: H (hydrogen) + O (oxygen) ? H2O (water). The simple word equation does not take into consider the conservation of matter, however.

Law of Conservation of Matter

• The law of conservation of mass states that standard chemical reactions do not create or destroy matter. If a reaction starts with 10 total atoms on one side, the end product must also contain 10 total atoms. In the water example, hydrogen and oxygen are naturally diatomic molecules: the hydrogen and oxygen molecules have two atoms that share electrons. To write the true word equation for water, the equation must take into consideration the diatomic nature of the hydrogen and oxygen molecules and be balanced to reflect the law of conservation of matter. The balanced equation for water looks like: 2H2 + O2 ? 2H2O. Each side of the equation has six atoms present: four hydrogen atoms and two oxygen atoms. The 2H2 has four hydrogen atoms; the O2 has two oxygen atoms. One compound of water is comprised of two hydrogen and one oxygen; two compounds of water -- denoted by 2H2O -- has four hydrogen and two oxygen, the same as the original reactants.