Stoichiometry (Quantitative Chemistry)

There is Qualitative Chemistry and Quantitative Chemistry
Under Quantitative Chemistry:

• Stoichiometry is a branch of chemistry that deals with the quantitative analysis chemical reactions
• It's a generalization of mole conversions to chemical reactions
• Understanding the 6 types of Chemical reactions is the foundation of stoichiometry

6 Types of Reactions

1. synthesis (formation)
2. Decompostion
3. Single Replacement (SR)
4. Double Replacement (DR)
5. Neutralization
6. Combustion

Synthesis

A+B>AB

• usually elements> compounds
• ex. K + O2 > 2K2O

Decomposition

AB>A+B

• Reverse of synthesis
• Always assume the compounds decompose into elements during decomposition
• Ex. 4H3PO4>6H2+P4 +8O2

Single Replacement (SR)

A+BC>B+AC

• ex. Ca+2KCL>2K+CaCl2

Double Replacement

AB+CD>AD+BC

• Ex. MgCl2+K2(SO4)>Mg(SO4)+2KCl

Neutralization (All DR)

Reaction between acid and base

• Ex. H2SO4+2KOH>2HOH+ K2SO4

Combustion

• Reaction of something (usually hydrocarbon) with air 
• Hydro carbon combustion always produces CO2 and H2O
• Ex. CH4+2O2>CO2+ 2H2O
• Always balance in the order C, H, then O

http://www.youtube.com/watch?v=XS6JTr-mTWY

Molecular Formulas

• If you know an empirical formula to find the molecular formula, you need the molar mass.

ex. The empirical formula for a substance is CH2O and its molar mass is 60.0 g/mol. Determine the molecular formula.

Empirical Formulas

• Empirical Formulas are the simplest formula of a compound
• Show only the simplest ratios, not the actual atom
• Example: the empirical formula for Chlorine gas is Cl
• Molecular formulas give the actual number of atoms

• To determine the empirical formula, we need to know the ratio of each atom
• To determine the ratio, fill in the table below:

ex, A sample of an unknown compound is found to contain 8.4 g of C, 2.1 g of H, and 5.6 g of O. Determine the empirical formula.

• The simplest ratio may be decimals. For certain decimals, you need to multiply everything by a common number.