1. Chapter 10 – Introduction to Equations
Writing and Balancing Equations Section 10.1

2. C8H18 + O2 -> CO2 + H2O + ENERGY
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!

3. Indicators of Chemical Reactions
Animation of Experiment (GIF Format, 321 k)
Temperature Change
Color Change
Odor
Production of Gas Bubbles
Production of a Precipitate

4. 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

5. Word Equations and Skeleton Equations
-Statements that indicate the reactants and products in a rxn
-Describe chemical reactions
-Lack important information
Iron (s) + chlorine (g) -> iron (III) chloride (s)
Skeleton Equations
-Uses chemical formulas to identify reactants and products
Fe (s) + Cl2 (g) -> FeCl3 (s)

6. Practice Problems
Write skeleton equations for the following word equations:
1. hydrogen (g) + bromine (g) -> hydrogen bromide (g)
H2 (g) + Br2 (g) -> HBr (g)
2. carbon monoxide (g) + oxygen (g) -> carbon dioxide (g)
CO (g) + O2 (g) -> CO2 (g)
3. potassium chlorate(s) -> potassium chloride(s) + oxygen(g)
KClO3 (l) -> KCl (s) + O2 (g)

7. A Balanced Chemical Equation
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… -> H2 + O2 -> 2H2O

8. Balancing Chemical Equations
There is a procedure for balancing chemical equations:
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
H Cl2 -> HCl

9. Balancing Equations Practice
Al + O2 -> Al2O
4Al + O2 -> 2Al2O
C3H8 + O2 -> CO2 + H2O
C3H8 + 5O2 -> 3CO H2O
KNO3 -> KNO2 + O2
2KNO3 -> 2KNO O2
O2 + CS2 -> CO2 + SO2
3O2 + CS2 -> CO SO2