1. Balancing Equations Review

2. What is a chemical equation?
Chemical equation - Describes a chemical change.
Parts of an equation:
2Ag + H2S
Ag2S + H2
Reactants
Products
Reactant - The chemical(s) you start with before the reaction.
Written on left side of equation.
Product - The new chemical(s) formed by the reaction.
Written on right side of equation.

3. Subscripts and Coefficients
Subscript - shows how many atoms of an element are in a molecule.
EX: H2O
2 atoms of hydrogen (H)‏
1 atom of oxygen (O)‏
Coefficient - shows how many molecules there are of a particular chemical.
EX: 3 H2O
Means there are 3 water molecules.

4. Law of Conservation of Mass
In a chemical reaction, matter is neither created nor destroyed.
In other words, the number and type of atoms going INTO a reaction must be the same as the number and type of atoms coming OUT.
If an equation obeys the Law of Conservation, it is balanced.

5. Rules of the Game Matter cannot be created or destroyed.
Subscripts cannot be added, removed, or changed.
You can only change coefficients.
Coefficients can only go in front of chem. formulas...NEVER in the middle of a formula.
If the same polyatomic is present on both sides of the equation, balance them as a unit, not as individual elements.

6. Determine the number of atoms for each element.
Steps:
Determine the number of atoms for each element.
Pick an element that is not equal on both sides of the equation.
Add a coefficient in front of the formula with that element and adjust your counts.
Continue adding coefficients to get the same number of atoms of each element on each side.

7. Examples Ca + O2  CaO Fe + O2  Fe2O3 C2H6 + O2  CO2 + H2O
Balance the following equations:
Ca O2  CaO
Fe + O2  Fe2O3
C2H6 + O2  CO2 + H2O
BaCl H2SO4  BaSO HCl