Chemical Equations

What Are Chemical Equations? A chemical equation is a short, easy way to show a chemical reaction, using symbols instead of words. Although chemical equations are shorter than sentences, they contain more information. Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction.

Formulas in an Equation All chemical equations use formulas to represent the substances involved in a reaction. A chemical formula is a combination of symbols that represents the elements in a compound. For example, CO2 is the formula for carbon dioxide. The formula tells you that this compound is made up of the elements carbon and oxygen and each molecule has 1 carbon atom and 2 oxygen atoms.

Formulas in an Equation The formula of a compound identifies the elements in the compound and the ratios in which their atoms are present.

Structure of an Equation All chemical equations have a common structure. A chemical equation tells you the substances you start with in a reaction and the substances you get at the end. The substances you have at the beginning are called the reactants. When the reaction is complete, you have new substances called the products.

Structure of an Equation The formulas for the reactants are written on the left, followed by an arrow. You read the arrow as “yields.” The formulas for the products are written on the right. When there are two or more reactants, they are separated by plus signs. In a similar way, plus signs are used to separate two or more products.

Structure of an Equation The number of reactants and products can vary. Some reactions have only one reactant or product. Other reactions have two, three, or more reactants or products. Here you can see the equation for a reaction that occurs when limestone (CaCO3) is heated. Count the number of reactants and products, and familiarize yourself with the parts of the equation.

Misconceptions Formulas and Equations Some students think that chemical formulas and chemical equations are the same, because formula and equation are sometimes used interchangeably in other subjects. In science a chemical formula describes a compound, and a chemical equation describes a reaction. ZnSO4 (Formula) Zn + H2SO4 → ZnSO4+ H2 (Equation)

Balancing Chemical Equations The principle of conservation of mass means that the same number of atoms exists in the products as in the reactants. To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation. Chemists say an equation is balanced when it accurately represents conservation of mass. How can you write a balanced chemical equation?

Balancing Act

Balancing Equations Atoms are not _______________ or _____________ during a chemical reaction. Scientists know that there must be the ___________ number of atoms on each ___________ of the ____________. To balance the chemical equation, you must add _______________ in front of the chemical formulas in the equation. You cannot _______ or ___________ subscripts!

Balancing Equations 1) Determine number of atoms for each element. 2) Pick an element that is not equal on both sides of the equation. 3) Add a coefficient in front of the formula with that element and adjust your counts. 4) Continue adding coefficients to get the same number of atoms of each element on each side.

Balancing Equations

Balancing Equations

Balancing Equations