Chapter 8 Notes
A CHEMICAL REACTION is the process by which one or more substances are changed into one or more
different substances. The original substances are known as the REACTANTS and the new substances
are the PRODUCTS. A chemical reaction can be written in the form of a CHEMICAL EQUATION. In a
chemical equation, the identities and molar amounts are represented for both the reactants and
products.
A chemical reaction can be identified by the following indicators.
1.
2.
3.
4.
Evolution of energy as heat or light
Production of a gas, normally visible in the form of bubbles
Formation of a PRECIPITATE, a solid produced as a result of a chemical reaction
Color change
Chemical equations can be written in WORD EQUATIONS, an equation in which the reactants and
products are presented by words. FORMULA EQUATIONS represent the reactants and products by
chemical symbols or formulas.
There are many additional symbols that are used in chemical equations. Rather than listing all these
symbols, they can be found on a chart on page 266 of the textbook.
In a chemical reaction all reactants and
products must be identified by the correct
formula for all substances involved in the
reaction. The LAW OF CONSERVATION OF
MASS must be satisfied. There must be the
same number of atoms of each element on
both the reactant side and the product side of
the chemical equation. This sometimes
requires the addition of COEFFICIENTS to the
chemical equation. Coefficients are small
whole numbers that appear in front of a
formula in a chemical reaction. This process of adding coefficients to a chemical equation is known as
BALANCING by inspection. Balancing equations can be easily mastered by following a step by step
process.
Identify the reactants and products, by writing the word equation.
1. Write the formula equation.
2. Balance the equation by the LAW OF CONSERVATION OF MASS.
a) Balance one element at a time.
b) Balance the elements that are combined and appear once on each side of the equation.
c) Balance polyatomic ions that appear on both sides as a single unit.
d) Balance Hydrogen and oxygen after all other atoms are balanced.
3. Count atoms to be sure that the equation is balanced.
Example:
Water  hydrogen + oxygen
H2O (l)  H2 (g) + O2 (g)
It is important to note that the physical state
of the compound or element is given in
paratheneses, (s) solid, (l) liquid, and (g)gas.
2H2O (l)  H2 (g) + O2 (g)
(partially balanced)
2H2O (l)  2H2 (g) + O2 (g)
(balanced)
Check atoms;
(Reactants)
4 hydrogens 2 oxygens  4 hydrogens + 2 oxygens
(Products)
Elements like hydroGEN, nitroGEN, oxyGEN, and haloGENs are known as diatomic elements.
This means that they will always bond to themselves in the form of H2, N2, or O2. AN EASY WAY
TO REMEMBER THIS IS ALL THE GENS.
There are thousands and thousands of different chemical reactions. These reactions can be
categorized into 5 basic types of reactions.
SYNTHESIS REACTION (composition reaction) - 2 or more substances are combined to form a
new compound.
A + X  AX
Common synthesis reactions are the reaction of elements with oxygen or sulfur. The
combination of elements with oxygen produces oxides.
2Mg + O2  2MgO
Magnesium + Oxygen  Magnesium Oxide
4Fe + 3O2  2Fe2O3
Iron (III) + Oxygen  Iron (III) Oxide
Non-metals can combine with oxygen in a synthesis reaction to form oxides.
C + O2  CO2
Carbon + Oxygen  Carbon Dioxide
Sulfur will combine with elements to form sulfides.
8Ba + S8  8BaS
Barium + Sulfur  Barium Sulfide
Metals will react with halogens in a synthesis reaction.
2Na + Cl2  2NaCl
Sodium + Chlorine  Sodium Chloride
Oxides of active metals (Group 1 and Group 2 metals) will react with water to form metal
hydroxides in a synthesis reaction.
CaO + H2O  Ca(OH)2
Calcium Oxide + Water  Calcium Hydroxide
A DECOMPOSITION REACTION breaks down a single compound into two or more simpler
substances. They are the opposite of synthesis reactions. Many of these reactions require
energy in the form of heat or electricity.
AX  A + X
ELECTROLYSIS is a decomposition reaction using an electric current to breakdown the
compound.
2H2O electricity> 2H2 + O2
Decomposition of Metal carbonates forms metal oxides and carbon dioxide.
CaCO3 heat> CaO + CO2
Calcium Carbonate heat> Calcium Oxide + Carbon Dioxide
Decomposition of metal hydroxides forms metal oxides and water.
Ca(OH)2 heat> CaO + H2O
Calcium Hydroxide heat> Calcium Oxide + Water
Decomposition of metal chlorates forms metal chlorides and oxygen.
2KClO3 heat> 2KCl + O2
Potassium Chlorate heat> Potassium Chloride + Oxygen
In a SINGLE DISPLACEMENT REACTION (replacement reaction), one element replaces a similar
element in the compound.
A + BX  AX + B
or
Y + BX  BY + X
An ACTIVITY SERIES is required in single displacement reactions. An activity series is a list
elements according to their reactivity or ease in which an element undergoes a chemical
reaction. The more reactivity elements will displace
elements of lower reactivity. A chart showing a typical
activity series is provided on page 286 of the textbook.
Metals can be displaced by other metals in a single
displacement reaction.
2Al + 3Pb(NO3)2  3Pb + 2Al(NO3)3
Aluminum is more reactive than lead so aluminum will
displace lead in the compound.
Hydrogen can also be displaced by a metal. Most group 1
metals react with water to form hydrogen and metal
hydroxides.
2Na + 2H2O  2NaOH + H2
In this case hydrogen form the water is displaced by the metal, sodium.
Hydrogen in an acid can also be displaced by a metal. Halogens can displace another halogen in
a displacement reaction. It is very important to remember that a single displacement reaction
is dependent of the activity series for elements.
In a DOUBLE DISPLACEMENT REACTION, the ions of two compounds exchange places to form
two form new compounds. This type of reaction can be identified by the formation of a
precipitate.
AX + BY  AY + BX
Sometimes a gas will be formed and bubbles will be observed. Water can be formed in a
double displacement reaction between an acid and a base.
A COMBUSTION REACTION involves the combination of oxygen with another substance,
releasing large amounts of energy in the form of light and heat. The formation of water is a
combustion reaction.
2H2 + O2  2H2O
The burning of fuels such as natural gas and petroleum products is also a combustion reaction.
C3H8 + 5O2  3CO2 + 4H2O
A combustion reaction of this nature will form carbon dioxide and water.