1. CHAPTER 8
CHEMICAL REACTIONS

2. Chemical Equations 8.1 Writing Chemical Equations
In a chemical reaction, starting substance(s) are changed into new substance(s).
REACTANT(S)  PRODUCT(S)

3. Bonds are broken and new bonds are formed, but atoms are not created nor destroyed.
Example of what law????

4. WAYS OF EXPRESSING A CHEMICAL EQUATION
Iron reacts with oxygen to produce rust (sentence)
Iron + oxygen  iron (III) oxide
(word equation)
Fe + O2  Fe2O3 (skeleton equation)
4Fe + 3O2  2Fe2O3 (balanced chemical equation)
The numbers above (4,3,2) are called COEFFICIENTS

5. ABOUT EQUATIONS 4Fe(s) + 3O2(g)2 Fe2O3(s)
Skeleton equation shows only the symbols and formulas.
The most correct equation includes the physical states of each substance.
4Fe(s) + 3O2(g)2 Fe2O3(s)
Study chart of symbols used in equations on page 206 in text.

6. CATALYSTS
A catalyst is used to speed up the rate of a chemical reaction but is NOT used up in the reaction.
A biological catalyst is called a(n) _____.
A substance that slows down the rate of a reaction is a(n) _________.

7. 8.2 TYPES OF CHEMICAL REACTIONS
Reactions are classified into five basic types. Some are combinations of these types.
Combination
Decomposition
Single-Replacement
Double Replacement
Combustion
On page 222 there is a great summary of these reactions.

8. COMBINATION REACTIONS (or synthesis)
Two or more substances combine to form a single substance
Basic equation
A + B → AB
If metal and non-metal combine, product is ionic
If two non-metals product is molecular

9. DECOMPOSITION REACTIONS
A single compound is broken down into two or more products
Basic equation
AB →A + B
Produces a combination of elements and compounds. Hard to predict.
Most require heat or light, or electricity

10. SINGLE REPLACEMENT RXNS
Atoms of one element replace the atoms of another element (single displacement)
Basic equation
A + BC → AC + B if A is a metal
A + BC → BA + C if A a non-metal

11. DOUBLE REPLACEMENT RXNS
Involves the changing of positive ions between two compounds (or negative ions)
Usually results in:
Formation of precipitate
Formation of a gas
Formation of water
Basic equation
AB + CD → AD + CB
Resembles FOIL from math class

12. COMBUSTION REACTIONS
A compound reacts with OXYGEN to produce energy in the form of heat and/or light.
When a hydrocarbon burns, the products are carbon dioxide and water.
Hydrocarbon + O CO2 + H2O

13. Can also combust other non-metals or metals
COMBUSTION REACTIONS
Incomplete combustion occurs with limited oxygen supply. Products of incomplete combustion are carbon monoxide and water.
Danger
Can also combust other non-metals or metals
Do you remember the burning magnesium?

14. 8.3 REACTIONS IN AQUEOUS SOLUTIONS
Many reactions take place in aqueous systems (including biological ones)
Can write various kinds of equations to describe these reactions

15. Complete molecular equation-
describes double replacement reaction
Complete ionic equation-
more accurately shows the reacting species as ions and the products either as ions or a precipitate
Net ionic equation-
focuses only on the ions REACTING
Spectator ions are those ions that do NOT participate in the reaction

16. PREDICTING THE FORMATION OF A PRECIPITATE
Consider the possibility that a precipitate may form.
Must use the solubility table on page 227 to decide.
Possible outcomes
No visible reaction (nvr)
Formation of one ppt.
Formation of two ppt. (rare occurrence)