1. Formulas, Equations, and Moles
Chapter 03: Formulas , Equations, and Moles
Formulas, Equations, and Moles

2. Atomic and Molecular Mass
The atomic masses as tabulated in the periodic table are the averages of the naturally occurring isotopes.
Mass of C = average of 12C and 13C
= x 12 amu x amu
= amu

3. Atomic and Molecular Mass
The mass of a molecule is just the sum of the masses of the atoms making up the molecule.
m(C2H4O2) = 2·mC + 4·mH + 2·mO
= 2·(12.01) + 4·(1.01) + 2·(16.00)
= amu

4. Avogadro and the Mole
One mole of a substance is the gram mass value equal to the amu mass of the substance.
One mole of any substance contains 6.02 x 1023 units of that substance.
Avogadro’s Number (NA, x 1023) is the numerical value assigned to the unit, 1 mole.

5. Avogadro and the Mole
The Mole: Allows us to make comparisons between substances that have different masses.

6. Balancing Chemical Equations
A balanced chemical equation represents the conversion of the reactants to products such that the number of atoms of each element is conserved.
reactants  products
limestone  quicklime + gas
Calcium carbonate  calcium oxide + carbon dioxide
CaCO3(s)  CaO(s) + CO2(g)

7. Balancing Chemical Equations
CaCO3(s)  CaO(s) + CO2(g)
The letters in parentheses following each substance are called State Symbols
(g) → gas (l) → liquid (s) → solid (aq) → aqueous

8. Balancing Chemical Equations
A balanced equation MUST have the same number of atoms of each element on both sides of the equation.
H2 + O2 → H2O Not Balanced
2H2 + O2 → 2H2O Balanced

9. Balancing Chemical Equations
The numbers multiplying chemical formulas
in a chemical equation are called:
Stoichiometric Coefficients (S.C.)
2H2 + O2 → 2H2O Balanced
Here 2, 1, and 2 are stoichiometric coefficients.

10. Balancing Chemical Equations
Hints for Balancing Chemical Equations:
Save single element molecules for last.
Try not to change the S.C. of a molecule containing an element that is already balanced.
If possible, begin with the most complex molecule that has no elements balanced.

11. Balancing Chemical Equations
Hints for Balancing Chemical Equations:
4) Otherwise, trial and error!!

12. Balancing Chemical Equations
Example 1: CH4 + O2 → CO2 + H2O
Balance O2 last
C is already balanced
Start by changing S.C. of H2O to balance H
CH4 + O2 → CO2 + 2H2O

13. Balancing Chemical Equations
Example 1: CH4 + O2 → CO2 + 2H2O
Now C and H are balanced
Balance O by changing the S.C. of O2
CH4 + 2O2 → CO2 + 2H2O
BALANCED!

14. Balancing Chemical Equations
Example 2: B2H6 + O2 → B2O3 + H2O
Balance O last
B is already balanced
Start by changing S.C. of H2O:
B2H6 + O2 → B2O3 + 3H2O

15. Balancing Chemical Equations
Example 2: B2H6 + O2 → B2O3 + 3H2O
B and H are balanced
Balance O by changing S.C. of O2
B2H6 + 3O2 → B2O3 + 3H2O
BALANCED!