What is a Chemical Reaction?

Chemical reactions are taking place all around us. Some are spectacular and really fun to watch, while others are difficult to even realize a chemical reaction has occured. A chemical reaction occurs when one or more substances are changed into one or more new substances by the reorganization of component atoms.  In a chemical reaction, reactants contact each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products.

In a chemical reaction, atoms are neither created nor destroyed. All atoms present in the reactants must be accounted for in the products. 

The reactant is the starting substance shown to the left of the reaction arrow.

The product is the new substance formed by the chemical reaction, and is found on the right of the reaction arrow.

The new product has different chemical and physical properties from the original reactants.

The creation of water is an example of a chemical reaction. The chemical formula for water is shown here.

Chemical reactions give clues that they are occurring and often give clues. The following is a list of several indicators that a chemical reaction has occurred. You may see one indicator, more than one, or even all of them during a chemical reaction.

Chemical Reaction

A permanent change in color.

A solid forms.

This is called a precipitate.

precipitate
chemical change

Gas is released. 

Change in temperature or a flame is produced. In addition, light energy will be given off.

chemical reaction
bad odor

An odor is produced. This may be pleasant like  baking a cake or very foul.