Video 9-1
• Reaction Stoichiometry
• Steps for Problem Solving
CHAPTER 9
STOICHIOMETRY
I. Reaction Stoichiometry
 Review:
 Change the following into moles:
 34.8 grams of hydrogen (MM = 1.0079)
 7.35 x 1025 molecules of water
I. Reaction Stoichiometry
 Using BALANCED CHEMICAL
EQUATIONS, you can determine
mass (or particle or mole)
relationships between reactants and
products in a chemical reaction.
I. Reaction Stoichiometry
a XY + b QZ  c AB + d CD
Particles XY
Moles XY
Grams XY
Moles QZ
Moles AB
Moles CD
I. Reaction Stoichiometry
a XY + b QZ  c AB + d CD
 Mole ratios come from the
COEFFICIENTS in the balanced
equations.
II. Steps for Problem Solving
1. Determine the products of the
reaction and write the complete
equation.
2. Balance the equation.
3. Determine what you are LOOKING
FOR (“WANTED”)
4. Determine what you are starting with
(“GIVEN”).
II. Steps for Problem Solving
5. Use dimensional analysis to change the
“given” into the “wanted”.
 Ex.
How much oxygen is required to burn 20.35
grams of methane (CH4)? How many
grams of each product are formed?
NOTE: This problem assumes you have an
unlimited (excess) amount of oxygen.
Video 9-2
• Limiting Reactants
• Percent Yield
III. Limiting Reactants
(Reagents)
 Limiting Reactant—limits the amount
of product formed. Also determines
how much of the other reactant
(excess reactant) can be used in the
reaction.
 Stoichiometric quantities: all
reactants are exactly used up (no
excess reactants)
III. Limiting Reactants
(Reagents)
 2 ways to determine which is the
limiting reactant:
 A. Determine how much of the
second reactant is needed to use up
the first one.
1. Select one of the reactants. Change it
into moles.
2. Change those moles into moles of the
second reactant.
III. Limiting Reactants
(Reagents)
3. Change moles into the unit given for
that second reactant (grams, molecules,
etc.).
4. Compare this quantity with the given
quantity for this reactant. If you have
this much, the first reactant can all be
used up  1st reactant is limiting
reactant.
III. Limiting Reactants
(Reagents)
 B. Determine how much product
each reactant can produce.
1. Change the given quantity of each
reactant into MOLES of one of the
products (choose the same product for
both conversions).
2. Whichever reactant produces the LEAST
amount of product is the limiting
reactant.
III. Limiting Reactants
(Reagents)
 Ex.
If 15.0 grams of oxygen and 5.00 grams
of hydrogen react, how many grams
of product will be produced? How
much excess reactant will be left
over?
IV. Percent Yield
 Theoretical yield: CALCULATED
amount of product that should be
produced from a given chemical
reaction
 Actual yield: measured amount of
product obtained from the reaction
when it is actually done.
IV. Percent Yield
 Sometimes (due to errors in actually
conducting the reaction), theoretical
yield  actual yield
 Percent yield = (actual yield /
theoretical yield) x 100%
Given in problem or
determined by actually
doing the reaction
CALCULATED using
stoichiometry and
methods learned earlier
IV. Percent Yield
 Ex.
A student reacts 15.0 grams of oxygen
with 5.00 grams of hydrogen. The
student obtains 15.5 grams of
product. What is the percent yield of
the reaction?
IV. Percent Yield
 Ex.
How much product is collected from the
reaction between 25.34 grams of nitrogen
and excess hydrogen if the percent yield is
87.34%?