1. Chemical Reactions, Chemical Equations, and Stoichiometry
Brown, LeMay Ch 3
AP Chemistry

2. 3.2: Types of reactions
Precipitation: formation of insoluble precipitate(s); more of this in Chapter 4
Combustion: rapid reactions that produce a flame; hydrocarbon combustion always produces CO2 and H2O. If insufficient O2, CO is produced; more of this in Chapter 25
Acid/base: exhibit no change in oxidation number for any species (ionic or molecular) involved; many special cases; more in Ch

3. Redox: electrons are transferred from one reactant to the other; change in oxidation number; more in Ch. 20
Complexation: a central metal ion has a characteristic number of surrounding molecules or ions bonded to it; more in Ch. 24

4. 3.3: Atomic, Molecular & Formula Weights
Atomic mass units:
1 amu = x g
or 1 g = x 1023 amu
1 atom of 12C isotope defined as weighing exactly 12 amu
Average atomic mass (or atomic weight):
12C: % x 12 amu =
13C: 1.108% x amu =
11.867
AW = amu
Therefore g C = 1 mol C

5. Molecular mass or weight (MM or MW): sum of atomic masses of each atom in the chemical formula. Ex: H2SO4
MW = (2)(1.0079) (4)(16.00) = amu
Formula weight (FW): same as MW, except for ionic substances in which no “molecule” exists. Then, FW is the simplest integer ratio of moles of each element (ions) present. Ex: NaCl is a 3D array of ions
FW = = amu

6. 3.4 – 3.7: Mass Relationships Percent Composition:
Ex: What is the percentage of oxygen in phosphoric acid?

7. The Mole and Molar Mass (MM)
From Latin moles: “a mass”
Avogadro’s Number = x 1023 atoms in exactly g of 12C = 1 mol
Converting: grams → moles → molecules
Ex: How many molecules of H2O in g H2O?
= x 1024 molecules H2O

8. C:H mole ratio is 6.7:20. ≈ 1:3. So, empirical formula is CH3,
Empirical Formula: simplest integer ratio of moles (or atoms) of each element present
Ex: What is the empirical formula of a compound that is composed of 80.% Carbon and 20.% Hydrogen? If the molecular weight is found to be 30 g/mol, what is the molecular formula?
Strategy: Assume 100. g of unknown
C:H mole ratio is 6.7:20. ≈ 1:3. So, empirical formula is CH3,
and the molecular formula is C2H6.

9. Limiting Reagent (or reactant):
Ex: If 6.0 g hydrogen gas reacts with 40.0 g oxygen gas, what mass of water will be produced?
2 H2 (g) + O2 (g) → 2 H2O (g)
O2 is limiting reagent, H2 is excess.

10. Percent yield & Percent error:
Ex: If in the previous example, only 40.0 g water were formed, what is the percent yield and percent error?