1. Chemical Reactions What is a chemical reaction?
When substances go through a chemical change and form new substances with different properties.
What are some examples of chemical reactions?
Rusting of iron
Souring of milk
Burning of paper
Cooking an egg

2. 2 Parts of a chemical reaction:
Na + Cl  NaCl
________: substances that enter into a reaction
Answer: Reactants
________: substances produced by a reaction
Answer: Products
Example: What are the reactants and products in the rusting of iron?
Reactants
Iron, water and oxygen
Products
Rust

3. How does a chemical reaction occur?
An atom will try to get 8 valence electrons by breaking existing bonds and rearranged to form new bonds.
A convenient way to express a chemical reaction is by writing a chemical equation:
reactants yields product
4Fe O  Fe2O3
coefficients

4. Law of Conservation of Mass Video
In a closed system, matter can not be created or destroyed during a chemical reaction (it can only be rearranged).
The total mass of the reactants EQUALS the total mass of the products.
Law of Conservation of Mass Video
Example:
2H O2  2H2O
If the total of 5 grams of Hydrogen and Oxygen gases were combined, then ______ of water would be obtained.
Answer: 5 grams

5. Balanced Chemical Reactions
A chemical equation must show that atoms are not created or destroyed (Law of Conservation of Mass).
Must have the same number of atoms on both sides of the arrow.
Is this equation balanced?
H O2  H2O
2H O2  2H2O

6. Balance the following equations by using
coefficients (“numbers in front of substances”)
a. Ag S  Ag2S
2Ag S  Ag2S
b. Al HCl  H AlCl3
2Al HCl  3H AlCl3
c. KI  K I2
2KI  2K I2
d. K O2  K2O
4K O2  2K2O
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