Transcript Stoichiometry - Mrs. Wiedeman

Stoichiometry
Chapter 9
Stoichiometry
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1.
2.
Def: study of mass relationships in
chemical reactions
Mole conversions
Relationship between products and
reactants
Stoichiometry
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Revolve around balanced equations:
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Coefficients = # particles
# of MOLES of particles
2H2 + O2  2H2O
2 moles H2 + 1 mole O2  2 moles H2O
Stoichiometry
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MOLAR RATIOS!!
2H2 + O2  2H2O
Molar ratio of:
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H2 : O2?
H2 : H2O
O2 : H2O
Use these as conversion factors!
Mole-Mole Problems
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2H2 + O2  2H2O
How many moles of H2 are required to
react with 2.5 mole O2?
How many moles of Al(NO3)3 are produced
when .75 mol AgNO3 reacts with Al?
Mass-Mole Problems
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Fe2O3 + Al  Al2O3 + Fe
How many moles of Fe are produced when
5.50 g of Fe2O3 reacts?
How many moles of water are required to
react with .25 g of Na?
Mole-Mass Problems
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Mg + O2  MgO
How many grams of MgO can be produced
from 2.95 mol Mg reacting with oxygen?
F2 + KBr  KF + Br2
What mass of KBr is needed to react with
0.96 mol F2?
Mass-Mass Problems
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Sodium phosphate reacts with magnesium
nitrate
If you have 3.12g of magnesium nitrate,
how many grams of magnesium
phosphate will you produce?
Helpful Sites
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Mole - Mole
http://science.widener.edu/svb/tutorial/rxn
smolestomolescsn7.html
Mass - Mass
http://science.widener.edu/svb/tutorial/rxn
sgramstogramscsn7.html
Limiting Reactants
Limiting Reactants
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Amount of products depends on amount
of reactants
Car runs because gas reacts with O2
Out of gas = car doesn’t run
Gas = limiting reactant
Limiting Reactants
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Limiting reactant – reactant that limits
the amount of product
Amount of product will ONLY be amount
made from limiting reactant
Excess reactant – reactant that is not
used up completely
Finding the Limiting Reactant
1.
2.
3.
Balance the equation
Pick 1 product and calculate the amount
of product produced from both reactants
Reactant that produced the smallest
amount of product is limiting reactant
More about Limiting Reactants
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Fe + S  FeS
650. g Fe reacts with 650. g S, what is the
LR?
What is the mass of sulfur in excess?
http://www.chemcollective.org/applets/sto
ich.php
Finding the Limiting Reactant
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Cu + AgNO3  Cu(NO3)2 + Ag
If 3.1 mol Cu and 3.1 mol AgNO3 react,
what is the limiting reactant?
How many grams of Ag will be
produced?
Mass excess reactant unreacted?
Percent Yield
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Amount you calculate isn’t what you
always produce
Lab errors
Theoretical Yield – amount produced
based on calculations
Percent Yield
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Actual Yield – amount of product
“actually” obtained from lab
Percent Yield – percent of product you
actually recovered in lab
Percent Yield
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% Yield =
actual yield
x 100
theoretical yield
Percent Yield
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Pb(NO3)2 + KI  PbI2 + KNO3
Determine the % yield if 16.4 g Pb(NO3)2
reacts with 28.5 g KI if 18.3g PbI2 is
produced.