Stoichiometry
What do I get when I have????
What is Stoichiometry?
 a branch of chemistry that deals with the quantitative
relationships that exist between the reactants and
products in chemical reactions.
 Stoichiometry can be used to calculate quantities
such as the amount of products that can be produced
with given reactants and percent yield (the
percentage of the given reactant that is made into the
product).
In Other words
 How much product do I get when I mix certain
amounts of Reactants together,
 Or, How much do I need to make what I want.
Steps in Stoichmetry
Write the Balanced Chemical Equation.
2. Convert the grams given into moles.
3. Multiply by the mole ratio from the Balanced
Chemical Equation.
4. Convert the new number of moles to grams.
1.
Why did I have to learn the Mole
Equations?
 The second step in Stoichiometry requires
you to convert from grams to moles (or things
to moles)
 The fourth step in Stoichiometry requires you
to convert from moles to grams (or moles to
things)
Railroad Track Stoichiometry
The best way to learn is to do it
 So here we go: You have 5 grams of Lead
(II) Nitrate mixed with an excess of Sodium
Chloride, how many grams of Lead (II)
Chloride will you produce?
 Step 1, write the balanced equation:
 Pb(NO3)2+ 2 NaCl  PbCl2 + 2 NaNO3
Step 2: Convert grams to moles
Step 3: Multiply by mole ratio
Step 4: Convert back to grams
And the Answer is:
One More time
 You have 5 grams of Lead (II) Nitrate mixed
with an excess of Sodium Chloride, how
many grams of Sodium Nitrate will you
produce?
 Step 1, write the balanced equation:
 Pb(NO3)2+ 2 NaCl  PbCl2 + 2 NaNO3
Step 2: Convert grams to moles
Step 3: Multiply by mole ratio
Step 4: Multiply by New Molar Mass
And the Answer is:………
Moles instead of grams???
 In case of this, you can skip either step 2 or
step 4, YEAH!!!!!!!!!!!!
 How many moles of Lead (II) Nitrate are
needed to produce 6 grams of Sodium
Nitrate?
 Back to Step 1:
 Pb(NO3)2+ 2 NaCl  PbCl2 + 2 NaNO3
Starting in grams, so
 We still need Step 2:
Still have to do Step 3:
 Moles to Moles:
Limiting Reagent Problems
 Chemical Reactions will continue until one of
the Reagents (Reactants) is used up.
 Once one of the Reagents is used up, the
reaction stops!
 It doesn’t matter how much of the other one
(Excess) is still left, the reactions STOPS.
Limiting Reactants require TWO
complete Stoichiometry Equations
 One for each Reactant:
 SAME FOUR STEPS, Two times………..
 If 5.00 grams of Lead (II) Nitrate is reacted
with 5.00 grams of Sodium Chloride, what is
the Limiting Reactant (Reagent), and how
much of the solid product is produced?
 Same STEP 1:
 Pb(NO3)2+ 2 NaCl  PbCl2 (s) + 2 NaNO3
It is a gram to gram problem, so…
 You still have to do all the steps, but twice.
 Once for each reactant:
Continuing:
And…….
 5.00 g Lead (II) Nitrate makes 4.20 g of Lead
(II) Chloride.
 5.00 g Sodium Chloride makes 9.81 grams of
Lead (II) Chloride.
 So, Lead (II) Nitrate is the Limiting Reagent
because it makes the least Product.
 Sodium Chloride is the Excess Reagent, it
makes the most Product.
 Only the Least Amount can be made, so only
4.20 g of Lead (II) Chloride is produced.
YOU CAN ONLY MAKE THE …
 LEAST AMOUNT OF PRODUCT.
 A Car can only go as far as the Gasoline lets
it go!!!!!!!!!!!
Percent Yield
 Stiochiometry gives us a perfect answer in a
perfect world.
 In the Real World not every atom reacts.
 If you run your car out of gas, you can still
smell gasoline in the gas tank, some it still
left, but the car won’t run.
Percent Yield Formula
Example
 In a chemical reaction between Lead (II)
Nitrate and Sodium Chloride the
Stoichiometry determined that 4.20 grams
should be produced. When the Experiment
was actually performed, 3.95 grams was
produced. What is the Percent Yield?
 % yield = 3.95 g actual
4.20 g predicted
X 100 = 94.05 %