1. Ch. 9 Chemical Reactions Identifying a Chemical Change
Describing Chemical Change
Types of Chemical Reactions
Reactions in Aqueous Solution

2. Describing Chemical Change
Word equations
In a reaction, one or more substances (reactants) change into one or more new substances (products)
Reactants  Products
As reactants are converted to products, the bonds holding the atoms together are broken and new bonds are formed
Atoms are neither created nor destroyed, only rearranged
Observes the Law of Conservation of Mass

3. Describing Chemical Change
Chemical equations
The arrow in the equation, reactants  products, separates the formulas of the reactants from the formulas of the products
Skeleton equations
The first step in writing an equation – only contains proper formulas
Does not indicate amounts of reactants or products
Physical state may be included (s, l, g, aq)
Catalysts are written above the yield sign (pg. 206)

4. Describing Chemical Change
Balancing chemical equations
A complete chemical equation includes formulas, states, conditions and numbers of atoms involved
Coefficients are used to show the correct quantity of reactants and products
Placed in front of the reactants and products
If there is no coefficient, it is assumed to be 1
In every balanced equation, each side of the equation has the same number of atoms of each element

5. Evidence of a Chemical Rxn
5 Main evidences for a chemical change
Production of a gas
Precipitate
Production of water
Heat/Light
Production of a new substance.

6. Types of Chemical Rxns Classifying reactions
There are 5 general types of reactions
Combination (synthesis)
Decomposition
Single-replacement
Double-replacement
Combustion
Not all chemical reactions fit uniquely into only one of these classes
Sometimes, one rxn may fit 2 or 3 different types

7. Types of Chemical Rxns Combination reactions (synthesis)
Two or more substances combine to form a single product The product will always be a compound
Metal + nonmetal  ionic compound
Nonmetal + nonmetal  molecular compound
Sometimes, 2 nonmetals may produce more than one product
S + O2  SO2
2S + 3O2  2 SO3

8. Types of Chemical Rxns Decomposition reactions
A single compound is broken down into two or more products
Can be any combination of elements or compounds
It is usually very difficult to predict the products of decomposition reactions
Most decomposition reactions usually require energy in the form of heat, light, or electricity

9. Types of Chemical Rxns Single-replacement reactions
One element replaces a second element in a compound
Also known as single-displacement reactions
Whether one metal will replace another can be determined by the chemical reactivities of the two metals
The activity series lists the order of decreasing reactivity
A metal can replace any metal listed below it on the series

10. Types of Chemical Rxns Single-replacement reactions
A nonmetal can also replace another nonmetal in a compound
This replacement is usually limited to halogens
The activity of halogens decreases as you move down the group
Fluorine can replace any of the halogens, chlorine can replace any halogen beneath it, etc.

11. Types of Chemical Rxns Double-replacement reactions
Involve an exchange of positive ions between two reacting compounds
Generally take place between two ionic compounds in aqueous solution
Often characterized by the formation of a precipitate

12. Ch. 8.2 Types of Chemical Rxns
Combustion reactions
An element or compound reacts with oxygen, often producing energy in form of heat and light
These reactions commonly involve hydrocarbons, compounds of H and C
The complete combustion of a hydrocarbon produces CO2 and H2O (elemental O and toxic CO may be by-products)
If the supply of O2 is insufficient during the rxn, combustion will be incomplete
A large amount of heat is usually released

13. Types of Chemical Rxns Predicting products of a chemical reaction
Synthesis: A + B  AB
Decomposition: AB  A + B
Single-replacement: A + BX  AX + B
Double-replacement: AX + BY  AY + BX
Combustion: CxHy + O2  CO2 + H2O

14. Reactions in Aqueous Soln
Net ionic equations
Equations that show dissolved ionic compounds as their free ions
Ions not directly involved in the equation are called spectator ions
These appear on both sides of the equation, and can be ignored
The ions left over are those involved in the net ionic equation

15. Reactions in Aqueous Soln
Predicting formation of a precipitate
Mixing solutions of ionic compounds can sometimes lead to the formation of a precipitate
A precipitate is an insoluble salt
Solubility of salts depends on a number of factors
See Table for the Solubility Rules for Ionic Compounds