1. Types of Chemical Reactions

2. States of Chemicals All chemicals will be one of the following states:
Solid
Liquid
Gas
Aqueous:
Dissolved in water
From now on, unless otherwise stated, assume that you are required to include the states for each chemical in any question

3. Hints for predicting states:
1. Read the question carefully!
Often times the question will give away information regarding the states of many (if not all) chemicals involved
Pay attention to the following terms:
Precipitate = “solid”
Soluble = “aqueous”
2. The states for individual elements are given on the periodic table
On your table: look at the legend at the top of your table
Regular font = solid
Bold italic font = liquid
Bubble letter font = gas

4. Hints for predicting states:
3: For compounds, make note of the following:
Solids:
Unless otherwise stated, most ionic compounds are solid at room temperature
Gases:
Common sense and life experience should remind you that compounds such as carbon dioxide and carbon monoxide are gases

5. Hints for predicting states:
3: For compounds, make note of the following:
Liquids:
Only pure, molecular (covalent) compounds can be found as liquids
Alcohols and water are the only two we will come across
Water is the most common one you will work with regularly
Aqueous:
Anything that is dissolved in water (read question & use common sense)
All acids are always aqueous

6. Types of Chemical Reactions
There are only five (5) different types of chemical reactions:
1) Double Replacement
2) Single Replacement
3) Synthesis/Formation
4) Decomposition
5) Combustion

7. Reaction Type 1 – Double Replacement
Occur between two ionic compounds
Does not happen with covalent compounds
Involves an exchange of cations (positive ions)
The cation of one compound trades places with the cation of another compound to form two new compounds

8. Identifying a Double Replacement Reaction
Double replacement reactions always have two ionic compounds on the REACTANTS side AND on the PRODUCTS side of an equation
*Two compounds react to form two new compounds*
AB + CD  CB + AD
A & C are cations, B & D are anions
A & C switch places

9. Double Replacement - Characteristics
occur in solution when the compounds are in an aqueous state (aq)
reactants are either aqueous to begin with, or solid compounds dissolved in water to form an aqueous solution of ions
Both reactants MUST be dissolved in water
This allows the compounds to separate into their ions so that they can exchange/recombine
in order to drive the reaction, one of the products must be removed from the aqueous solution
this can occur via one of three ways:

10. Double Replacement - Characteristics
1) Formation of a precipitate (an insoluble solid forms in the solution)
i.e.:
Pb(NO3)2 (aq) + 2NaI (aq)  2NaNO3 (aq) + PbI2 (s)
Solid lead (II) iodide is formed as precipitate and comes out of the solution

11. Double Replacement - Characteristics
2) Water is formed when a hydrogen cation unites with a hydroxide anion
i.e.:
NaOH (aq) + HCl (aq)  HOH (l) + NaCl (aq)
Water (HOH) is formed and comes out of the solution

12. Double Replacement - Characteristics
3) Formation of a gas
i.e.:
FeS (aq) + 2HCl (aq)  H2S (g) + FeCl2 (aq)
Hydrogen sulfide gas is formed and comes out of the solution

13. 1) Formation of a Precipitate
Determining if a Double Replacement Reaction Occurs & Predicting the States of the Products
1) Formation of a Precipitate
Use a “Solubility Table”
Look at the compounds formed, and use a solubility table to identify if a precipitate is formed
Ion combination = “low solubility”
A precipitate is formed, state will be written as a solid in the products
Ion combination = “soluble”
No precipitate forms, state will be written as aqueous.
If both products are aqueous, NO REACTION OCCURS - You will simply have a mixture of ions

14. Determining if a Double Replacement Reaction Occurs & Predicting the States of the Products
2) Formation of water
If water is a product, it will be written as a “liquid”, not “aqueous” since it is a pure liquid
Yes, water is technically a covalent compound, however it is still present in double replacement reactions.
It is created when an H+ cation combines with a OH- anion
Sometimes it is helpful to write H2O as HOH symbolizing the joining of a H+ cation and an OH- anion
3) Formation of a gas
Solubility table is not helpful
More difficult to identify
Use your best judgment, or the info will be given in the question

15. What if both products are aqueous?
In this case, the reaction will NOT PROCEED or will NOT HAPPEN
Remember, in order for a double replacement reaction to occur, one of the products MUST leave the solution – if both products stay in solution, no reaction occurs
i.e. KCl (aq) + NH4CH3COO (aq)  KCH3COO (aq) + NH4Cl (aq)
NO REACTION