Download Chapter 3: Mass Relations:

Chapter 3: Mass Relations:
Stoichiometry: The study of mass
relations in chemistry
Stoichiometry
• All Stoichiometry is based on the Law of
Conservation of Mass
Section 11-1
3.1 Atomic Masses
• Atomic mass unit (AMU) is defined as 1/12th
the mass of a carbon – 12 atom.
• The weighted average of the masses of the
isotopes of an element create the elements
atomic mass.
– Remember completing weighted avg???
Atomic Mass vs. Molar Mass
• A.M.U works for theory, but we can not measure
individual atoms
• Must create molar mass.
• Avagadro’s number, number of atoms of carbon-12 it
takes to weigh exactly 12 grams.
• 6.02 x 1023 atoms = 1 mole
3.2 Mole Mountain #1
3.3 Percent Composition
• Remember the poison worksheet?
• What is the % of Carbon in glucose C6H12O6
3.4 Reaction Stoichiometry
• How do we know how much we need, how
much will be created.
• Think of a reaction as a recipe,
Reactants → Products
Must be a Balanced Equation
Mole Mt. # 2
Limiting Reactant
• Why do reactions stop?
– Eventually we run out of reactants
– The reactant we run out of first, stopping the
reaction, is the limiting reactant
– Any reactant that is left over is the excess reactant
If I have 400 tires, 150 engines, 200
steering wheels, and 300 bucket seats
(2 per car), how many complete cars
could I make?
What is the limiting reactant?
What is excess reactant?
S8(l) + 8Cl2(g) → 4S2Cl4(l)
200.0g S and 100.0g Cl2
Determine which is the limiting reactant
Percent Yield
• Reactions do not always produce all of what
they should.
• ____________ yield is how much should be
produced based on the limiting reactant
• ____________ yield is how much is actually
produced in an experiment
Percent Yield
Percent yield is important in the cost effectiveness of many
industrial manufacturing processes.
If you are supposed to make 100 pounds of aspirin, and only
produce 50 pounds, the company has now lost money.