1. Chapter 4
Chemical Reactions

2. Conservation of Mass
When a chemical reaction happens, atoms are not allowed to be created or destroyed.
If we start with 4.2g of 
substances, we must end 
with 4.2g of substances.
Law of Conservation of Mass – Law that states mass cannot be created in destroyed in ordinary chemical and physical changes.

3. Balanced Equation
To make sure that all of the mass and the matter is conserved, 
equations need to be balanced.
A balanced equation is one that has the same numbers and types of atoms on both the reactant side and the product side. O C O C C O O C C C O

4. Generally, the element symbol is placed in the middle column
Balanced Equation
To use a REP Table, each element 
must have a row of its own. Chemical Equation – a representation of a chemical that uses symbols to show the relationship between the reactants and the product O C
Reactant
Element
Product C O
Generally, the element symbol is placed in the middle column
In the Reactant and Product columns, the number of atoms of each 
element are written. When each element has matching numbers in both Reactant and Product columns, the equation is balanced.
Reactant – a substance or molecule that participates in a chemical reaction
Product- the substance that forms in a chemical reaction

5. Balanced Equation O C
Reactant
Element
Product 3 6 C O

6. Balanced Equation O C
3C + 2O3
3CO2
Reactant
Element
Product 3 6 C O

7. Balanced Equation Fe O
Reactant
Element
Product 1 2 3 Fe O

8. Balanced Equation Fe O
Reactant
Element
Product 4 6 Fe O

9. Does the following equation follow Conservation of Mass?14
Does the following equation follow Conservation of Mass?
[This object is a pull 

tab]
Answer No
Ca and C are not the same.
Yes No Ca Br C Br

10. Does the following equation follow Conservation of Mass?15
Does the following equation follow Conservation of Mass?
[This object is a pull 

tab]
Answer
Yes
Yes No Ca Br Br Ca

11. 16
Does the following equation follow Conservation of Mass?
[This object is a pull 

tab]
Answer
Yes
Yes No
2Na + Cl2
2NaCl