Download limiting reactants

8.3
Limiting Reactants
Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings
1
A limiting reactant in a chemical reaction is the
substance that
• Is used up first.
• Stops the reaction.
• Limits the amount of product that can form.
2
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?
Copyright © 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings
What is the limiting item?
3
limiting reactant:
is the reactant that limits the extent
of the reaction and determines the
amount of the product formed.
Excess reactants
 Reactants that leftover when a
reaction stops

Four table settings can be made.
Initially
plates
5
forks
6
spoons 4
knives
7
Use Left over
4
1
4
2
4
0
4
3
The limiting item is the spoon.
5
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
6
When 4.00 mol H2 is 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, H2 and Cl2.
•
The limiting reactant is the one that produces
the smaller amount of product.
7
HCl from H 2
4.00 mol H2 x 2 mol HCl = 8.00 mol HCl
1 mol H2
(not possible)
HCl from Cl 2
2.00 mol Cl2 x 2 mol HCl = 4.00 mol HCl
1 mol Cl2
(smaller number)
The limiting reactant is Cl2 because it is used up
first. Thus Cl2 produces the smaller number of
moles of HCl.
8
Initially
H2
Cl2
4.00 mol
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
9
If 4.80 mol Ca mixed with 2.00 mol N2, which is the
limiting reactant? 3Ca(s) + N2(g) → Ca3N2(s)
Moles of Ca 3 H 2 from Ca
4.80 mol Ca x 1 mol Ca3N2 = 1.60 mol Ca3N2
3 mol Ca
(Ca used up)
Moles of Ca 3 H 2 from N 2
2.00 mol N2 x 1 mol Ca3N2 = 2.00 mol Ca3N2
1 mol N2
(not possible)
All Ca is used up when 1.60 mol Ca3N2 forms. Thus,
Ca is the limiting reactant.
10
Calculate the mass of water produced when
8.00 g H2 and 24.0 g O2 react?
2H2(g) + O2(g)
2H2O(l)
11
Calculate the grams of H2 for 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
= 27.0 g H2O (smaller)
1 mol H2O
O2 is the limiting reactant.
12
practice
1- How many moles of CO2 can be produced by the
reaction of 5.0 grams of C2H4 and 12.0 grams of O2?
2- How many grams of carbon dioxide could be produced
from 2.0 g of C2H4 and 5.0 g of O2?
3- In the reaction between CH4 and O2, if 18.0 g of CO2 are
produced, how many grams of water are produced?
4- Cu + 2 AgNO3 → Cu(NO3)2 + 2 Ag.
When 50.0 g of copper was reacted with 300.0 g of silver
nitrate solution, 149 g of silver was obtained. What is the
percent yield of silver obtained?