Lesson 12
Chemical Equations
Lesson Glossary
balanced chemical equation
a reaction equation that has the same number of atoms of each element on both sides of
the equation
In Lesson 11 you studied chemical formulas. When chemical formulas are used to represent
substances in a reaction, you get a chemical equation. Chemical equations are used to represent
all reactions. In mathematics you work with equations. What you do to one side of the equation
must be done to the other side to keep the equation balanced. Similarly, in chemical equations
you need have the same number of atoms on each side to balance the equation.
Previously, you studied the neutralization reaction that occurs when you combine vinegar and
baking soda. If you were able to measure the mass of the reactants and then the mass of products
in this reaction, how do you think these masses would compare?
Experiments like the one involving vinegar and baking soda are similar to the experiments
Antoine Lavoisier performed. Lavoisier's experiments led to the development of the Law of
Conservation of Mass. In a chemical reaction the mass of the reactants is always equal to the
mass of the products.
Turn to page 52 of the textbook. Read introductory paragraphs of "Chemical Equations" and the
information in "The Law of Conservation of Mass." In "Try This!" the statement "Allow the gas
to escape" should read, "Do not allow the gas to escape."
1. What chemical did Antoine Lavoisier start with for his experiment?
2. What were the products of Antoine Lavoisier's experiment?
3. a. How is the experiment Antoine Lavoisier performed similar to the baking soda and vinegar
experiment described in the reading?
b. Name the law that describes the results of Antoine Lavoisier's experiment. What does this law
state?
Chemists use chemical equations to represent chemical reactions. These equations must be
balanced to show the proper proportion of reactants and products. Balancing an equation means
making sure an equation has the same elements and the same number of atoms of each element
on both sides.
Read "Staying Balanced" on page 53 of the textbook for further information on balanced
chemical equations.
4. Why do chemists use a chemical equation rather than a word equation to represent a reaction?
5. What is a subscript? What does a subscript tell you?
6. Complete question 2 of "Solve These" on page 53 of the textbook
7. What is a coefficient? What does the coefficient tell you?
8. Use the sample problem on page 54 of the textbook, to answer the following.
a.
b.
c.
d.
e.
f.
How many molecules of water are in the chemical equation?
How many molecules of oxygen are on the right side of the equation?
How many molecules of hydrogen are on the right side of the equation?
How many atoms of each substance are on the left side of the equation?
How many atoms of each substance are on the right side of the equation?
Is the equation balanced? Why?
9. Answer questions 1, 2, and 3 of "Solve These" on page 54 of the textbook. State the number of
atoms of each element on each side of the chemical equation.