1. Types of Chemical Reactions

2. About Chemical Reactions. . .
REMEMBER a chemical reaction is a process through which a chemical change takes place
-- chemical reactions start with one or more substances undergoing a chemical change to create new substances
-- the original substance(s) is/are called the reactants
-- the new substance(s) is/are called the products
A chemical reaction will ALWAYS produce a new substance
There are six different ways in which a new substance can be produced. . .
-- these are the six types of chemical reactions

3. Type #1: Synthesis Reactions
Synthesis reactions occur when 2 or more substances combine to form a larger, more complex compound
-- also called a combination reaction
-- also called an addition reaction
THERE WILL ONLY BE 1 COMPOUND AS A PRODUCT
Always follows the general equation:
A + B AB +

4. Examples of Synthesis Reactions
Example: Making Hydrochloric Acid (HCl)
Hydrogen gas and chlorine gas react to form hydrochloric acid:
H2 (g) + Cl2 (g) 2 HCl (l)
How do you easily identify a synthesis reaction?
-- Are there elements or simple (usually diatomic) compounds as reactants?
-- Is there only 1 compound as a product?
2 Mg (s) + O2 (g) 2MgO (s)

5. Type #2: Decomposition Reactions
Decomposition reactions are the opposite of synthesis reactions
Large compounds break down into smaller compounds or elements
THERE IS ALWAYS ONLY 1 REACTANT
Always follow the general formula:
AB A + B +

6. Examples of Decomposition Reactions Mg(ClO3)2 (s) MgCl2 (s) + 3O2 (g)
Example: Breakdown of mercury (II) oxide
Mercury (II) oxide decomposes to form liquid mercury and oxygen gas
HgO (s) Hg (l) + O2 (g)
How do you easily identify a decomposition reaction?
-- Is there only 1 compound for a reactant?
-- Are there multiple elements or compounds as products?
Mg(ClO3)2 (s) MgCl2 (s) + 3O2 (g)

7. Type #3: Single-Displacement Reactions
In a single-displacement reaction, one element replaces another element in a compound
-- a metal will always replace another metal
-- hydrogen will always replace a metal
-- a nonmetal will always replace a nonmetal
These are also called single replacement reactions
Always follows the general formula:
A + BC AC + B + +

8. Examples of Single-Displacement
Example: The single-displacement of zinc and hydrogen
Aqueous hydrochloric acid reacts with zinc metal to form zinc chloride and hydrogen gas:
Zn (s) + 2 HCl (aq) ZnCl2 (s) + H2 (g)
Example 2: The single-displacement of chlorine and bromine
Aqueous sodium bromide reacts with chlorine gas to form sodium chloride and liquid bromine
Cl2 (g) + 2NaBr (aq) 2 NaCl (aq) + Br2 (l)

9. Type #4: Double-Displacement Rxns
Also called double replacement reactions
Always occurs between two ionic compounds, both of which are usually aqueous (solid dissolved in solution)
-- the ions “switch partners”
-- the cation of one compound partners with the anion of the other compound
Always follows the general formula:
AB + CD AD + CB + +

10. Requirements for Double-Displacement
For a double-displacement reaction to occur:
-- both reactants need to be ionic compounds
-- one of the products must be insoluble
Because double-displacement reactions happen between reactants that are aqueous ionic compounds, one of the products must no longer be aqueous
Either:
-- a precipitate will form
-- a gas will form (bubbles will appear)
-- water will be a product

11. Examples of Double-Displacement
Example: Lead (II) nitrate and potassium iodide
Aqueous lead (II) nitrate reacts with potassium iodide to form lead (II) iodide and potassium nitrate
Pb(NO3)2 (aq) + KI (aq) PbI2 (s) + 2KNO3 (aq)
Example #2: Barium and Potassium
Aqueous barium chloride reacts with aqueous potassium carbonate to form barium carbonate and potassium chloride
BaCl2 (aq) + K2CO3 (aq) BaCO3 (s) + 2KCl (aq)

12. Type #5: Combustion Reactions CxHy + O2 (g) CO2 (g) + H2O (l) + heat
Combustion reactions are a special type of reaction which involve the burning of a hydrocarbon in oxygen gas
-- the products are ALWAYS water and carbon dioxide
-- heat is also given off as a byproduct
Combustion reactions always follow the general formula:
CxHy + O2 (g) CO2 (g) + H2O (l) + heat H H H + + H H H H H

13. Examples of Combustion Reactions
Example: The burning of methane gas (Bunsen burner)
Methane gas reacts with oxygen gas to form carbon dioxide, water, and heat
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (l) + heat
How do you easily identify a combustion reaction?
-- look for a hydrocarbon and oxygen as reactants
-- look for water and carbon dioxide as products
C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (l)

14. Type #6: Acid-Base Reactions HBr (aq) + KOH (aq) KBr (aq) + H2O (l)
Acid-base reactions are a special type of double-displacement reaction where a hydrogen cation in one reactant and a hydroxide anion in the other reactant combine to form water as a product:
Example: The neutralization of hydrogen bromide with potassium hydroxide
Hydrogen bromide (hydrobromic acid) reacts with potassium hydroxide (a base) to form potassium bromide (a salt) and water
HBr (aq) + KOH (aq) KBr (aq) + H2O (l)

15. Identifying Acid-Base Reactions
How do you easily identify acid-base reactions?
-- look for a basic double-displacement reaction
-- look for the hydroxide ion in the reactants (OH)
-- look for water as a product

16. Identify the Following Reaction Types
2CH3OH (l) + 3 O2 (g) 3 CO2 (g) + 4 H2O (l)
FeS (aq) + 2 HCl (aq) H2S (aq) + FeCl2 (s)
PbO2 (s) Pb (s) + O2 (g)
Cl2 (g) + 2 NaI (s) 2 NaCl (s) + I2 (g)
SO2 (s) + H2O (l) H2SO3 (aq)