Chemical Reactions



There are thousands of different chemical
reactions that can take place in nature and
in industrial processes
It would be difficult to memorize all of
them!
By classifying reactions, we can predict
the products that will form
Types of Reactions
•
These are the types of chemical
reactions we will talk about:
1.
2.
3.
4.
5.
•
Synthesis reactions
Decomposition reactions
Single displacement (replacement) reactions
Double displacement(replacement) reactions
Combustion
You need to be able to identify the type
of reaction and predict the product(s)
Steps to Writing Reactions
Step 1
Identify the type of reaction from clues that are
available. Write a word equation.
Example: The combustion of methane gas in air
forms water and carbon dioxide.
Word equation:
Methane + oxygen  water + carbon dioxide
Step 2







Write a generic equation following the rules from
Reaction Types.
Write the reactants and products using
appropriate symbols and formulas.
Balance charges for ionic compounds using the
Common Ion Chart or Periodic Table.
Don’t forget diatomic elements! (BrINClHOF).
Example:
Methane + oxygen  water + carbon dioxide
CH4 + O2  H2O + CO2
Step 3



Balance the equation by adjusting the
coefficients.
Example: CH4 + O2  H2O + CO2
Balanced: CH4 + 2O2  2H2O + CO2
Step 4







Confirm that the equation is balanced by
checking the number of atoms of each element
on both sides of the equation.
Example: CH4 + 2O2  2H2O + CO2
Reactants
Products
1C
1C
4H
4H
4O
2O + 2O = 4O
This equation is balanced!
1. Synthesis reactions
•
•
Synthesis reactions occur when two
substances (sometimes elements) combine
and form a compound. (Sometimes these are
called combination or addition reactions.)
reactant + reactant  1 product
Basically: A + B  AB
•
•
Example: 2H2 + O2  2H2O
Example: C + O2  CO2
Synthesis Reactions
•
Here is another example of a synthesis
reaction
Practice
•
•
•
•
Predict the products. Write and balance
the following synthesis reaction equations.
Sodium metal reacts with chlorine gas
Na(s) + Cl2(g) 
Solid Magnesium reacts with fluorine gas
Mg(s) + F2(g) 
Aluminum metal reacts with fluorine gas
Al(s) + F2(g) 
2. Decomposition Reactions
•
•
•
•
•
Decomposition reactions occur when a
compound breaks up into the elements or
in a few to simpler compounds
1 Reactant  Product A+ Product B
In general: AB  A + B
Example: 2 H2O  2H2 + O2
Example: 2 HgO  2Hg + O2
Decomposition Reactions when heated






Metallic Carbonates give off metallic oxide and
Carbon Dioxide:
Li2CO3  Li2O + CO2
Metallic Hydroxides give off metallic oxide and
water:
Ba(OH)2  BaO + H2O
Metallic Chlorates give off metallic chloride
and O2:
2 NaClO3  2 NaCl + 3 O2
Mineral Acids make water and nonmetal
oxide:
H2CO3  H2O + CO2
Metal Oxides release O2: 2PbO2  2PbO + O2
Electrolysis breaks compounds into elements:
2KCl  2K + Cl2
2. Decomposition Reactions
•
Another view of a decomposition reaction:
3. Single Replacement Reactions
A + BX  B + AX
•
•
Active Metals replacing metals forming a
salt. (Check the Activity Series) Na > Ag
Na˚ + AgNO3  Ag˚ + NaNO3
More Single Replacement Reactions
•
•
•
Very Active Metals react w/ water releasing
H2 and metallic hydroxide
(check Activity Series):
2K + 2H2O  H2 + 2KOH
Metals and Acids form H2 and salts:
Zn + 2 HCl  H2 + ZnCl2
Halogen-Halide Replacement
(check Activity Series):
F2 + 2RbBr  Br2 + 2RbF
Single Replacement Reactions
•
Aluminum metal reacts with Copper II Nitrate
Al
+ Cu(NO3)2 
4. Double Replacement Reactions
•
Double Replacement Reactions occur
when a metal replaces a metal in a compound
and a nonmetal replaces a nonmetal in a
compound
•
Compound + compound  product + product
•
AB + CD  AD + CB
Double Replacement Reactions
•
•
•
Think about it like “foil”ing in algebra, first and
last ions go together + inside ions go together
Example:
AgNO3(aq) + NaCl(s)  AgCl(s) + NaNO3(aq)
Another example:
K2SO4(aq) + Ba(NO3)2(aq)  2 KNO3(aq) + BaSO4(s)
Practice
•
Predict the products. Be sure to check the
charges. Balance the equation
1.
HCl(aq) + AgNO3(aq) 
2.
CaCl2(aq) + Na3PO4(aq) 
3.
Pb(NO3)2(aq) + BaCl2(aq) 
4.
FeCl3(aq) + NaOH(aq) 
5.
H2SO4(aq) + NaOH(aq) 
6.
KOH(aq) + CuSO4(aq) 
5. Combustion Reactions
•
•
Combustion reactions occur
when a hydrocarbon reacts with
oxygen gas.
This is also called burning!!! In
order to burn something you need
the 3 things in the “fire triangle”:
1) Fuel (typically hydrocarbon)
2) Oxygen (supports combustion)
3) Ignition energy (spark or heat)
Combustion Reactions
•
•
•
In general:
CxHy + O2  CO2 + H2O
Products in combustion are
ALWAYS carbon dioxide and
water. (although incomplete
burning does cause some byproducts like carbon monoxide)
Combustion is used to heat
homes (Methane, CH4) and run
automobiles (Octane, C8H18)
Combustion
•
Example
•
•
C5H12 + 8 O2  5 CO2 + 6 H2O
Write the products and balance the
following combustion reaction:
•
C10H22 + O2 
Mixed Practice
•
1.
2.
3.
4.
5.
State the type, predict the products,
check the charges and balance the
following reactions:
BaCl2 + H2SO4 
C6H12 + O2 
Zn + CuSO4 
Cs + Br2 
FeCO3 
Solubility Table
Determining Reaction Types
Identifying Reactions and Predicting Products
Identifying Reactions and Predicting Products
Identifying Reactions and Predicting Products