Stoichiometry - Mrs. Wiedeman
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Transcript Stoichiometry - Mrs. Wiedeman
Stoichiometry
Chapter 9
Stoichiometry
1.
2.
Def: study of mass relationships in
chemical reactions
Mole conversions
Relationship between products and
reactants
Stoichiometry
Revolve around balanced equations:
Coefficients = # particles
# of MOLES of particles
2H2 + O2 2H2O
2 moles H2 + 1 mole O2 2 moles H2O
Stoichiometry
MOLAR RATIOS!!
2H2 + O2 2H2O
Molar ratio of:
H2 : O2?
H2 : H2O
O2 : H2O
Use these as conversion factors!
Mole-Mole Problems
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
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
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
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
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
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
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
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
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
Amount you calculate isn’t what you
always produce
Lab errors
Theoretical Yield – amount produced
based on calculations
Percent Yield
Actual Yield – amount of product
“actually” obtained from lab
Percent Yield – percent of product you
actually recovered in lab
Percent Yield
% Yield =
actual yield
x 100
theoretical yield
Percent Yield
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.