1. Chapter 7 Chemical Reactions
7.2 Chemical Equations
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

2. Chemical Equations A chemical equation
Gives the chemical formulas of the reactants on the left of an arrow and the products on the right.
Reactants Product
O2(g)
CO2 (g)
C(s)
Copyright © by Pearson Education, Inc. Publishing as Benjamin Cummings

3. Chemical Equations are Balanced
In a balanced chemical reaction
Atoms are not gained or lost.
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

4. Chemical Equations are Balanced
In a balanced chemical reaction
The number of reactant atoms is equal to the number of product atoms.
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

5. Symbols Used in Equations
Symbols are used in
equations to show
The states of the reactants.
The states of the products.
The reaction conditions.
Table 7.2
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

6. A Balanced Chemical Equation
In a balanced chemical equation,
There must be the same number of each type of atom on the reactant and on the product sides of a balanced equation.
Numbers called coefficients are used in front of one or more formulas.
Al S Al2S Not Balanced
coefficients
2Al S Al2S3 Balanced
2Al = Al
3S = S

7. Learning Check State the number of atoms of each element on the
reactant and on the product sides of the equations:
A. P4(s) + 6Br2(l) → 4 PBr3(g)
B. 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)

8. Solution State the number of atoms of each element on the
reactant and on the product sides of the equations:
A. P4(s) + 6Br2(l) → 4PBr3(g)
4 P 4 P
12 Br Br
B. 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)
2 Al 2 Al
2 Fe Fe
3 O 3 O

9. Learning Check Determine if each equation is balanced or not.
A. Na(s) + N2(g) → NaN3(s)
B. C2H4(g) + H2O(l) → C2H5OH(l)

10. Solution Determine if each equation is balanced or not.
A. Na(s) + N2(g) → NaN3(s)
No. 2N on reactant side, 3N on product side.
B. C2H4(g) + H2O(l) → C2H5OH(l)
Yes. 2 C = 2 C
6 H = 6 H
1 O = 1 O