Chapter 17 Section 2

Balancing Chemical Equations

17.1 Products and reactants• In chemical reactions, you start with

reactants that are combined to make products.– The reactants are the starting substances.– The products are the new substances which

result from the chemical reaction.

17.1 Reactants and products• In the reaction, methane (a natural gas) is burned or

combusted. • Some energy is added to get the reaction started.

17.2 Conservation of mass• Lavoisier showed that a

closed system must be used when studying chemical reactions.

• When chemicals are reacted in a closed container, you can show that the mass before and after the reaction is the same.

17.2 Chemical Equations

• When a chemical reaction is written using chemical formulas and symbols, it is called a chemical equation.

17.2 Chemical equations

• An arrow is always included between reactants and products.

• It means “to produce” or “to yield.”

Reactants Products

to produce

“Methane combines with oxygen gas to produce carbon dioxide gas and water vapor.”

17.2 Numbers in equations

17.2 Balancing equations• The law conservation of mass is applied by balancing

the number and type of atoms on either side of the equation.

17.2 Balancing equations

• Counting atoms is necessary to balance an equation.

How many hydrogen atoms?

How many oxygen atoms?

How many carbon atoms?

17.2 Steps for balancing

1. If not provided, write the word form of the equation.– Calcium carbonate reacts with hydrochloric acid to produce

calcium chloride, carbon dioxide and water.

17.2 Steps for balancing

2. If not provided, write the chemical equation from the word form.

17.2 Steps for balancing3. Count the number of each type of atom on

both sides.

As in the video:

1.First balance the metals.2.Next balance the nonmetals.3.Lastly balance the H and O.