1. Chemical Reactions
Conservation of
Mass

2. Law of Conservation of Mass
In a chemical change, matter is neither created or destroyed.
Mass of Reactants = Mass of Products
# of Reactant Atoms = # of Product Atoms

3. Conservation of Mass

4. Counting Atoms

5. Atoms are Conserved in a Chemical Reaction
The identities (formulas) of the compounds must never be changed in balancing chemical equations.
DO NOT change the Subscripts.
You may only change the coefficients in an equation to balance the equation.

7. Steps To Balancing an Equation
Here are the basic steps to follow when balancing equations. You should always use pencil when balancing equation so that you can erase any mistakes.
1st  Count the atoms of each element on each side of the arrow in an equation.
Ex. CH4 + O2  CO2 + H2O
C = 1 C = 1
H = 4 H = 2
O = 2 0 = 3

8. Steps To Balancing an Equation
2nd We need to add compounds to get equal numbers of each element. You can only add whole amounts of a molecule.
Ex. CH4 + O2 + O2  CO2 + H2O + H2O
C = 1 C = 1
H = 4 H = 4
O = 4 O = 4

9. Steps To Balancing an Equation
The correct way to write this is to put a coefficient to represent multiple molecules or formula units.
- A coefficient is placed before a molecule.
- A coefficient pertains to every element in the compound, regardless of parenthesis.
Ex. CH4 + 2O2  CO2 + 2H2O
C = 1 C = 1
H = 4 H = 4
O = 4 O = 4
The equation is now balanced because there are equal amounts of carbon, hydrogen, and oxygen on the reactant side and on the product side.

10. Na + Br2  NaBr

11. Ca(OH)2 + HNO3  Ca(NO3)2 + H2O

12. Al2O3  Al + O2