1. Chemical Reactions
Chapter 2
Section 1 & 2

2. Physical Background
Physical Property: Characteristics of matter that can be seen through direct observations
Density
Melting point
Boiling Point
Physical Change: Change in which the identity of the substance does not change

3. Chemical Background
Chemical Property: characteristics of matter that can only be observed when one substance changes into a different substance
Iron to Rust
Chemical Change: New Substance is formed

4. A Change of Properties
The properties of these substances are very different from the starting substances
In a chemical reaction, bonds are broken. Atoms are then rearranged to form new substances

5. Signs of a Chemical Reaction
Gas
Solid
Energy
Endothermic
Exothermic
Color change

6. Chemical or Physical Glass Breaking Hammering wood together
Burning Leaves
Melting Ice
Frying an egg
Melting butter
Bleaching your hair
Fireworks
Mixing salt with water

7. Chemical Formula
A shorthand way to use chemical symbols and numbers to represent a substance
Shows how many of each atom is present in a molecule
3H2O
Subscript 2 – (applies to symbol before it)
Coefficient 3 – (applies to entire molecule)

8. Be Accurate Symbols can be mistaken!!

9. Chemical Equations
Use chemical symbols and formulas as a shortcut to describe a chemical reaction
Reactants = starting material
Products = substances formed from a reaction
C + O2  CO2
reactants before arrow products after arrow

11. Law of conservation of mass
During a reaction, mass is neither created nor destroyed
Equations must be balanced because atoms are neither created nor destroyed
Mass of Reactants = Mass of Products

12. How to balance an equation
Step 1
Count the number of atoms on each side
Step 2
You can only add or change coefficients to balance the number of atoms on each side.

13. Chemical Equation Shows the reaction between reactants and products
Reactants-starting material
Products-what is formed
C + O CO2
C=1 C=1
O=2 O=2