Name _____________________________________________________ Period ______
Elements and Compounds in Chemical Equations
A chemical reaction can take place when two or more substances react to form new substances.
New substances are formed when the atoms in the substances are rearranged. A chemical
equation shows us which substances are reacting (the reactants) and what new substances are
being made (the products). The reactants are shown on the left and the products are shown on the
right. For example: hydrogen and oxygen can react to form water as shown in the equation below.
hydrogen + oxygen water
2H2 + O2 2H2O (You can disregard the numbers in the equations during this activity.)
Some of the substances in an equation are elements and some are compounds. In the equation
above, hydrogen and oxygen are elements and water is a compound. The number of elements and
compounds in the reactants, the products, and in the entire equation can be seen in the table below.
Elements
Compounds
Reactants
2
0
Products
0
1
Total
2
1
Let’s see if you can identify the elements and compounds in some common chemical equations.
Photosynthesis is the process by which plants take in carbon dioxide, water, and sunlight to make
glucose and oxygen. The chemical equation follows.
6CO2 + 6H2O + light energy C6H12O6 + 6O2
Fill in the chart below with the correct number of elements and compounds in the reactants, the
products, and in the entire equation.
Elements
Compounds
Reactants
Products
Total
Respiration is the process by which you take in food (glucose) and oxygen for the purpose of
releasing energy that you can use. Carbon dioxide and water are also produced. Look at the
equation below and then fill in the chart with the appropriate numbers of elements and compounds.
C6H12O6 + 6O2 6CO2 + 6H2O + energy
Elements
Compounds
Reactants
Products
Total
