8.3 limiting reactants_2
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Chapter 8 Chemical
Quantities in Reactions
8.3
Limiting Reactants
Copyright 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings
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Limiting Reactant
A limiting reactantin a chemical reaction is the
substance that
Is used up first.
Stops the reaction.
Limits the amount of product that can form.
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Reacting Amounts
In a table setting, there is 1
plate, 1 fork, 1 knife, and
1 spoon.
How many table settings are
possible from 5 plates, 6 forks,
4 spoons, and 7 knives?
What is the limiting item?
Copyright 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Reacting Amounts
Four table settings can be made.
Initially Use Left over
plates 5 4 1
forks 6 4 2
spoons 4 4 0
knives 7 4 3
The limiting item is the spoon.
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Example of Everyday Limiting
Reactant
How many peanut butter sandwiches could be
made from 8 slices bread and 1 jar of peanut
butter?
With 8 slices of bread, only 4 sandwiches
could be made. The bread is the limiting item.
Copyright 2008 by Pearson Education, Inc. publishing as Benjamin Cummings
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Example of Everyday Limiting
Reactant
How many peanut butter sandwiches could be
made from 8 slices bread and 1 tablespoon of
peanut butter?
With 1 tablespoon of peanut butter, only 1sandwich could be made. The peanut butter is
the limiting item.
Copyright 2008 by Pearson Education, Inc. publishing as Benjamin Cummings
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Limiting Reactants
When 4.00 mol H2is mixed with 2.00 mol Cl2,how
many moles of HCl can form?
H2(g) + Cl(g) 2HCl (g)
4.00 mol 2.00 mol ??? mol
Calculate the moles of product from each
reactant, H2and Cl2.
The limiting reactant is the one that produces
the smaller amount of product.
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Copyright 2008 by Pearson Education, Inc. publishing as Benjamin Cummings
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Limiting Reactants Using
MolesHCl from H2
4.00 mol H2 x 2 mol HCl = 8.00 mol HCl
1 mol H2 (not possible)
HCl from Cl22.00 mol Cl2x 2 mol HCl = 4.00 mol HCl
1 mol Cl2 (smaller number)
The limiting reactant is Cl2because it is used up
first. Thus Cl2produces the smaller number of
moles of HCl.
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Checking Calculations
Initially H2
4.00 mol
Cl2
2.00 mol
2HCl
0 mol
Reacted/Formed
-2.00 mol -2.00 mol +4.00 mol
Left after
reaction
2.00 mol
Excess
0 mol
Limiting
4.00 mol
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Limiting Reactants Using Mass
If 4.80 mol Ca mixed with 2.00 mol N2, which is the
limiting reactant? 3Ca(s) + N2(g) Ca3N2(s)
Moles of Ca3H2from Ca
4.80 mol Ca x 1 mol Ca3N2= 1.60 mol Ca3N23 mol Ca (Ca used up)
Moles of Ca3H2from N2
2.00 mol N2x 1 mol Ca3N2 = 2.00 mol Ca3N21 mol N2 (not possible)
All Ca is used up when 1.60 mol Ca3N2forms. Thus,
Ca is the limiting reactant.
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Limiting Reactants Using Mass
Calculate the mass of water produced when
8.00 g H2 and 24.0 g O2react?
2H2(g) + O2(g) 2H2O(l)
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Limiting Reactants Using Mass
Calculate the grams of H2for each reactant.
H2:
8.00 g H2 x 1 mol H2 x 2 mol H2O x 18.02 g H2O
2.016 g H2 2 mol H2 1 mol H2O
= 71.5 g H2O (not possible)
O2:
24.0 g O2 x 1 mol O2 x 2 mol H2O x 18.02 g H2O
32.00 g O2 1 mol O2 1 mol H2O= 27.0 g H2O (smaller)
O2is the limiting reactant.
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