1. Law of Conservation of Mass
In a chemical reaction, matter is not created or destroyed
This means that you have to have the same number of each type of atom on each side of the chemical equation.
After you write a chemical equation you have to balance it to make sure that the same number of atoms of each element are on each side.

2. SO3 = 1 sulfur & 3 oxygen 3SO3 = 3 sulfur & 9 oxygen
Balancing Equations
TIPS
A coefficient is the number placed in FRONT of an element or compound. Coefficients are used to balance the number of atoms on each side.
2H2O - coefficient is 2
When counting atoms you multiply the compound by the coefficient.
SO3 = 1 sulfur & 3 oxygen SO3 = 3 sulfur & 9 oxygen

3. NEVER change subscripts for a compound or polyatomic ion
Balance oxygen LAST

5. Steps 1. Complete an atom inventory CH4 + O2  CO2 + H2O 1 1 C H 4 2 O C H O

6. ___CH4 + ___O2  ___CO2 + ___H2O
2. Add coefficients to make the atoms balance
___CH4 + ___O2  ___CO2 + ___H2O C H O 2 2 4 4 4

7. **another TIP…. look for 2/3 pattern, balance that atom first**
Practice
**another TIP…. look for 2/3 pattern, balance that atom first**
Write a balanced chemical equation for the reaction in which aluminum reacts with oxygen to produce aluminum oxide.
____Al 4
+ ___O2 3
 ___Al2O3 2 4 Al O 4 6 6

8. Write a balanced chemical equation for the reaction in which hydrochloric acid reacts with calcium carbonate to produce calcium chloride, water, and carbon dioxide.
__HCl 2
+ __CaCO3
 __CaCl2
+ __H2O
+ __CO2 2 H Cl Ca C O 2

9. __BeF2 + __ Al2O3  __ BeO+ __ AlF3 Be F Al O 3 6 6 2 3

10. __PbO + __HCl  __H2O + __PbCl2 Pb O H Cl 2 2