STOICHIOMETRY
- the study of the
quantitative
aspects off
chemical
reactions.
STOICHIOMETRY
It rests on the principle of the conservation of
matter.
2 Al(s) + 3 Br2(l) ------> 2 AlBr3(s)
PROBLEM: If 454 g of ammonium
nitrate decomposes, how many grams of
H2O are formed? N2O is other product.
STEP 1
W it the
Write
th balanced
b l
d chemical
h i l
equation
1 NH4NO3 ----->
> 1 N2O + 2 H2O
Remember the coefficients are
equal to the mole ratios
Page 1
454 g of NH4NO3 --->
> N2O + 2 H2O
STEP 2 Convert mass reactant -->
--> moles of
reactant
STEP 3 Convert moles reactant -->
--> moles
product
product--using coefficients
STEP 4 Convert moles product
product--->
> grams
of product
454 g NH4NO3 1 mol NH4NO3 2 mol H2O
18.0 g H2O =
80.0 g NH4NO3 1 mol NH4NO3 1mol H2O
Answer = 204 g H2O (theoretical yield)
GENERAL PLAN FOR
STOICHIOMETRY
CALCULATIONS
Mass
product
Mass
reactant
Moles
reactant
Stoichiometric
factor (Mole ratio)
Moles
product
Percent Yield
„
„
Theoretical yield is the term used when you
determine the maximum product that can be
made-this is done by using stoichiometry.
Experimental yield is the term used for the
amount that is actually made (usually some is
lost through human error)
„
„
Experimental yield is either given in the problem
directly, or enough data is given so that you can
determine it
Percent yield = experimental yield x 100
theoretical yield
Page 2
.776 g of Tetracarbon decahydride is
combusted in excess oxygen.
If 1.00 g of water is made what is the
percent yield?
First write the balanced equation (complete
combustion of a hydrocarbon creates water and
carbon dioxide as products).
products)
8 CO2 + 10 H2O
2 C4H10 + 13 O2
„ Now set up mass-mass problem to find
theoretical yield for water
„
.776 g C4H10 1mol C4H10 10 mol H2O 18.0 g H2O =
58.1 g C4H10 2 mol C4H10 1 mol H2O
Answer = 1.20 g H2O = theoretical yield
Finishing the problem
„ Experimental
Yield = 1.00 g
water
„ Theoretical
h
i l Yield
i ld = 1.20 g water
„ % Yield = 1.00 / 1.20 x 100 =
83.3 % yield
Page 3