1. Chemical Reactions

2. Chemical Reactions and Equations
A chemical reaction occurs when the atoms of one or more substances are rearranged to form completely new substances

3. Evidence for Chemical Reactions
When a chemical reaction occurs there are typically several signs that a chemical change is happening
Color change
Solid is formed from two liquids
Heat is given off
Light is given off

4. Representing Chemical Reactions
In every chemical reaction there are reactants and products
Reactants are the starting materials
Products are the new compounds that are formed
Reactant1 + Reactant2
Product1 + Product2

5. Chemical Equations contd.
In chemical equations, chemical symbols or formulas are used to show which elements or compounds are participating in the reaction
Examples:
NaOH + HCl  NaCl + H2O
AgNO3 + HCl  AgCl + HNO3
Mg + O2  MgO

6. Balancing Chemical Equations
Let's take a look at our previous reactions:
NaOH + HCl  NaCl + H2O
AgNO3 + HCl  AgCl + HNO3
Mg + O2  MgO
According to the law of conservation of mass,
mass can neither be created nor destroyed, therefore
we must balance the equation to show this

7. Types of Chemical Reactions

8. Single Replacement
Single replacement reactions occur when a single element reacts with a compound
One element replaces another to form a new compound
Example:
Mg HCl  MgCl2 + H2

9. Double Replacement
Double replacement reactions occur when two compounds react
The ions in each compound simply swap places with each other
Example:
CaCl2 + Na2CO3  CaCO NaCl

10. Combustion
Combustion reactions occur when one of the reactants is oxygen.
Oxygen (O2) has to be a reactant and not a product
Example:
C3H O2  3 CO H2O

11. Synthesis
Synthesis reactions occur when two or more reactants react to create only one product
Example:
2 Na + Cl2  2 NaCl

12. Decomposition
Decomposition reactions occur when one reactant reacts to form two or more products.
These are basically the opposite of a synthesis reaction
Example:
2 NaClO3  2 NaCl O2