Page 266 - Science Course 3 (Book 1)

Mo7-L4b: What are Chemical Equations?

Chemical formulas and other symbols are parts of a
Mo7-L4b What are Chemical Equations? chemical equation.

KEY CONCEPTS: Reactants are the Products are any new
1. Why are chemical equations useful? substances that are substances formed
2. What are some factors that affect the rate of present before a during a chemical
chemical reactions? chemical reaction reaction.
Reactants Product

Fe + S FeS
Vocabulary A-Z

Let us learn some vocabulary A plus sign separates The arrow is read as
two reactants or “yields“. It separates
products the reactants and the
Concentration products and indicates
the amount of a particular solute in a given amount that a reaction that a
of solution. reaction has taken
place.
The formulas to the left of the arrow represent the
reactants—the substances present before the
reaction takes place.

The formulas to the right of the arrow represent the
products—the new substances present after the
reaction.

The arrow indicates that a reaction has taken place.
Concentrated Diluted

2C H + 5O 2 4CO + 2H O
2
2
2
2
Let’s Begin

Explaining Chemical Reactions

Chemical changes often are called chemical reactions. In a chemical equation, the number of atoms of each
element before a reaction must equal the number of
A useful way to understand what happens during a atoms of each element after the reaction.
chemical reaction is to write a chemical equation.
This is called a balanced chemical equation, and it
A chemical equation shows the chemical formula of illustrates the conservation of mass.
each substance in the reaction.
When balancing an equation, you cannot change the
chemical formula of any reactants or products.
2H + O 2 2H O
2
2
H H O H

H O
CH 4 + 20 2 CO 2 + 2H O +
2
H O H O H
H

4 Hydrogen atoms 4 Hydrogen atoms
+ +
2 oxygen atoms 2 oxygen atoms
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