1. Chemical Formulas
Coefficient Subscript #of molecules 5CO2 #of atoms

2. Chemical Reactions-
takes place when chemical bonds between atoms are broken and new bonds form. There are the same number of total atoms of each element at the end.

3. Chemical Equations- Ex) Na + Cl NaCl reactants products
Reactants - the chemicals to be combined
(left of the arrow)
Products - Results of the combinations
(right of the arrow)
Ex) Na + Cl NaCl
reactants products

4. 3 Rules to Balancing Equations
1. Check to make sure all formulas
are written correctly.
2. Do NOT change subscripts in
formulas.
Only change coefficients.

5. A coefficient of 2 must be placed in front of Na to be balanced!
Coefficients-
Numbers placed in front of a formula to make the number of atoms on each side of the equation equal.
Ex) Na + Cl NaCl
Na is NOT equal!
A coefficient of 2 must be placed in front of Na to be balanced!
2Na + Cl NaCl

6. Count atoms, then begin with an element that only occurs once on each side of an equation.
Ex. A)
H H2O
Which element is not equal?
1. H2 +O H O =
H ≠
2H2 + O H2O balanced!

7. Ex. B) Na + 2H20 NaOH + H2 Which element is not equal?
Coefficient of 2 added to NaOH
Na + 2H NaOH + H O= H= Na ≠
2Na + 2H NaOH + H2

8. 4 Types of Chemical Reactions
Synthesis Reaction
Reaction in which two or more substances combine to forms a compound.
Sodium + Chloride Salt
2Na + Cl NaCl

9. Decomposition Reaction
Compound breaks into two or more substances.
2HgO Hg + O2

10. Single Replacement Reaction
One element replaces another element in a compound to form a new compound
Fe + CuSO FeSO4 + Cu

11. Double Replacement Reaction
Occurs when two compounds in a reaction exchange atoms
AgNO3 + NaCl AgCl + NaNO3