HONORS CHEMISTRY
Feb 27, 2012
Brain Teaser
Cu + 2 AgNO3  2 Ag + Cu(NO3)2
– How many moles of silver are produced when
25 grams of silver nitrate reacts with excess amount
of copper?
– How many grams of silver nitrate are needed to
produce 50 grams of silver?
Agenda
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Brain Teaser
Notes: Limiting Reactants
Work on Mixed Stoichiometry Practice Worksheet 2
Homework
– Complete Worksheet
Limiting Reactants
Limiting Reactants
• Reactant that is completely used up in a
chemical reaction
• Determines the maximum amount of product
that can be formed.
Limiting Reactants
• Why is this important?
– The quantities of products formed in a reaction
are always determined by the quantity of the
limiting reactant.
Limiting Reactants
• Analogy: making cheese sandwiches
Limiting Reactants
Limiting Reactants
Limiting Reactants
2H2 + O2  2H2O
What is the limiting reactant?
Limiting Reactants
2H2 + O2  2H2O
What is the limiting reactant?
Limiting Reactants
• How many grams of water can I make from 22
grams of hydrogen and 195 grams of oxygen?
– Write a balanced chemical equation
H2 + O2  H2O
– What is the limiting reactant?
• Answer: Do two stoichiometry calculations
– Determine mass of product produced by each reactant
– How do you know?
Determining the limiting reactants
• The limiting reagent may not be obvious!!
Practice Problem
• If 11.3 grams of sodium chloride are formed in the
reaction described above, what is the percent yield of
this reaction?
Can you really get out everything that goes
in?
% yield = experimental yield x 100
theoretical yield
Experimental or actual yield determined in the
lab
Theoretical or expected yield determined by
stoichiometry
Practice Problem
• If 35 grams of C6H10 reacts with 45 grams of
oxygen, how many grams of carbon dioxide
will be formed?
– What is the limiting reactant?
– How much of the excess reactant is left over after
the reaction ?
– If 35 grams of carbon dioxide are actually formed
from the reaction, what is the percent yield of this
reaction?
Partner Quiz
1)
CaCl2 + Na2CO3  CaCO3 + 2NaCl
5.45 g
4.55 g
?
How much CaCO3 (in g) is formed? What is the
percent yield for this reaction if 3.96 g of calcium
carbonate was isolated from the reaction?