CHEMICAL EQUATIONSDOE-HDBK-1015/1-93Fundamentals of ChemistryCH-01Rev. 0Page 40ChemicalEquationsThe chemical equation is simply a representation of a chemical reaction in the chemist'sshorthand. In a chemical equation, the substances originally present are called the reactants andthe new substances being formed are called the products. In the chemical reaction, the reactantsare on the left of the arrow and the products are on the right of the arrow. For example, whenlooking at the combination of hydrogen and oxygen into water, the water molecule would bethe product on the right. 2H + O 2H O2 2 2If looking at the decomposition of water, the hydrogen and oxygen would be the products andthe water is the reactant. The arrow means yields and is used to separate the reactants from theproducts. It also indicates the direction of the reaction as illustrated below.2H O 2H + O2 2 2The single arrow in the above equation implies that the reaction will proceed in only onedirection until it subsides or stops. If the reaction is reversible, that is, it can proceed left toright and right to left until it reaches an equilibrium, then a double arrow is used. 2H O ? 2H + O2 2 2When writing an equation, always place the reactant on the left and the products on the righteven in the case of a reversible reaction. A chemical equation represents not only the reaction, but also shows the number of atoms ormolecules entering into and produced by the reaction. The formulas must be balanced correctlybased on the valences of the constituent elements. BalancingChemicalEquationsThe number of atoms or molecules of each substance is shown by the coefficients in theequation. Because atoms cannot be created or destroyed in a chemical reaction, a chemicalequation must be balanced so that there are exactly the same number of atoms of each elementon each side of the equation.
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business