1. Counting Atoms and Balancing Chemical Equations

2. If there is not a subscript listed, it is understood to be 1.
Subscripts
C12H22O11
There are 12 atoms of Carbon
There are 22 atoms of Hydrogen
There are 11 atoms of Oxygen
If there is not a subscript listed, it is understood to be 1.
NaCl
There is one atom of Sodium
There is one atom of Chlorine

3. Learning Check NaHCO3 HCl Sodium – 1 Hydrogen – 1 Carbon – 1 Oxygen -3
Chlorine - 1

4. There are times you will see a compound with parenthesis.
Pb(NO3)2
The 2 after the parenthesis indicates there are two sets of the parenthesis.
Pb(NO3) (NO3)
So, in counting the atoms, you would have the following:
Lead – Oxygen – Nitrogen -2

5. Learning Check (NH4)3PO4 Mg(OH)2 Nitrogen – 3 Magnesium – 1
Hydrogen – 12
Phosphorus – 1
Oxygen – 4
Mg(OH)2
Magnesium – 1
Oxygen – 2
Hydrogen – 2

6. Hydrogen – 4 Sulfur – 2 Oxygen – 8
Coefficient
2H2SO4
This means there are 2 compounds of sulfuric acid. Think:
H2SO4 + H2SO4
Counting the atoms:
Hydrogen – Sulfur – 2 Oxygen – 8
Coefficient

7. Learning Check 3H3PO4 2H2O Hydrogen – 9 Hydrogen – 4 Phosphorus – 3
Oxygen - 12
2H2O
Hydrogen – 4
Oxygen - 2

8. Reading Chemical Equations
The mass of all the reactants (the substances going into a reaction) must equal the mass of the products (the substances produced by the reaction).
CH4 + 2O2 → CO2 + 2 H2O
Reactants
Products

9. Law of Conservation of Mass
In a chemical reaction, matter cannot be created or destroyed. It can only be changed.
The reactants MUST contain the same elements and the same number of each element as the product. They CAN be in different compounds.

10. Do the following equations follow the law of conservation of mass?
Learning Check
Do the following equations follow the law of conservation of mass?
H2 + O H2O
Na + O Na2O
Mg + 2HCl MgCl2 + H2
HgO Hg + O2
N2 + 3H2 2NH3
2Na + 2H2O NaOH + H2
Zn + 2HCl ZnCl2 + H2 NO
YES

11. You must add coefficients to balance this equation:
Balancing Equations
Na + O2 → Na2O
For this equation to be balanced, there must be equal amounts of Na in the reactants and products.
You must add coefficients to balance this equation:
2Na + O2 → Na2O

12. Balancing Equations
Two ways…
M. I. N. O. H. or
Number charts

13. Balancing Equations
Two ways…
M. I. N. O. H.

14. M - Metals Add coefficients first
Balance metals such as Fe or Na first.

15. M - Metals I - Ions Add coefficients first
Balance metals such as Fe or Na first.
Second
I - Ions
Looks for polyatomic ions (such as PO4-3 or SO4-2) that cross from reactant to product unchanged. Balance polyatomic ions as a group within its parentheses.

16. M - Metals I - Ions N - Non-metals Add coefficients first
Balance metals such as Fe or Na first.
Second
I - Ions
Looks for polyatomic ions (such as PO4-3 or SO4-2) that cross from reactant to product unchanged. Balance polyatomic ions as a group within its parentheses.
Third
N - Non-metals
Chlorine (Cl) or Sulfur (S) are common non-metals to look for!

17. M - Metals I - Ions N - Non-metals O - Oxygen Add coefficients first
Balance metals such as Fe or Na first.
Second
I - Ions
Looks for polyatomic ions (such as PO4-3 or SO4-2) that cross from reactant to product unchanged. Balance polyatomic ions as a group within its parentheses.
Third
N - Non-metals
Chlorine (Cl) or Sulfur (S) are common non-metals to look for!
Fourth
O - Oxygen
Remember, oxygen by itself is O2

18. M - Metals I - Ions N - Non-metals O - Oxygen H - Hydrogen
Add coefficients first
M - Metals
Balance metals such as Fe or Na first.
Second
I - Ions
Looks for polyatomic ions (such as PO4-3 or SO4-2) that cross from reactant to product unchanged. Balance polyatomic ions as a group within its parentheses.
Third
N - Non-metals
Chlorine (Cl) or Sulfur (S) are common non-metals to look for!
Fourth
O - Oxygen
Remember, oxygen by itself is O2
Fifth (last)
H - Hydrogen
Remember, hydrogen by itself is H2

19. Balancing Equations
Two ways…
Number charts

20. Balancing Equations __H2 + __O2  __H2O 2 2 O - H - 2 4 O - H - 1 2 2

21. Balancing Equations __H2SO4 + __NaOH  __H2O +__Na2SO4 2 2 Na - SO4 –1 3 2 4
Na -
SO4 –
O –
H - 2 1 2 4

22. Balancing Equations __C3H8 + __O2  __CO2 +__H2O 5 3 4 C - O – H – 3 210
C -
O –
H – 1 3 2 3 7 10 8