Chapter 10 –
Introduction to Equations
Writing and Balancing Equations
Section 10.1
Chemical Reactions

One or more substances are rearranged to form
different substances
C8H18 + O2 -> CO2 + H2O + ENERGY
LOOK, IT’S A HYDROCARBON!!!!! The products are
carbon dioxide and water!
Indicators of Chemical Reactions






Temperature Change
Color Change
Odor
Production of Gas Bubbles
Production of a Precipitate
Animation of Experiment
(GIF Format, 321 k)
Representing Chemical Reactions
Symbol
Meaning
+
Separates two or
more reactants or
products
->
Separates reactants
from products
(s)
Solid state
(l)
Liquid state
(g)
Gaseous state
(aq)
Water solution



Statements called
equations are used to
describe what happens
during a chemical
reaction
Reactants are the
starting substances found
on the left side of the
equation
Products are the
substances formed during
a reaction
Word Equations and Skeleton
Equations
Word Equations
Skeleton Equations
-Statements that indicate the -Uses chemical
reactants and products in a formulas to identify
rxn
reactants and
-Describe chemical reactions products
-Lack important information
Fe + Cl
-> FeCl
(s)
Iron
(s)
+ chlorine
(g)
-> iron (III) chloride
(s)
2 (g)
3 (s)
Practice Problems
Write skeleton equations for the following word
equations:
1. hydrogen
(g)
+ bromine
H2
(g)
(g)
+ Br2
-> hydrogen bromide
(g)
-> HBr
2. carbon monoxide
(g)
+ oxygen
CO
(g)
+ O2
(g)
(g)
(g)
(g)
-> carbon dioxide
-> CO2
(g)
3. potassium chlorate(s) -> potassium chloride(s) + oxygen(g)
KClO3
(l)
-> KCl
(s)
+ O2
(g)
(g)
Balancing Equations
Chemical Equations also must obey the Law of
Conservation of Mass. The number of atoms that
are used in the reactants must equal the number of
atoms found in the products. Matter can neither be
created nor destroyed. A chemical equation that
follows the law of conservation of mass is called a
balanced chemical equation.
A Chemical Equation
H2 + O2 -> H20
A Balanced Chemical Equation
Coefficient… ->
2H2 + O2 -> 2H2O
Balancing Chemical Equations
There is a procedure for balancing chemical
equations:
1.
2.
3.
4.
5.
Write the equation (remember your diatomic molecules)
Count the atoms of each element
Add or adjust the coefficients (subscripts cannot be changed)
Reduce coefficients to lowest possible terms
Check your work
Hydrogen + Chlorine Yields Hydrochloric Acid
H2 + Cl2 -> HCl
Balancing Equations Practice
Al + O2 -> Al2O
4Al + O2 -> 2Al2O
C3H8 + O2 -> CO2 + H2O
C3H8 + 5O2 -> 3CO2 + 4H2O
KNO3 -> KNO2 + O2
2KNO3 -> 2KNO2 + 2O2
O2 + CS2 -> CO2 + SO2
3O2 + CS2 -> CO2 + 2SO2