Chapter 10 – Part 2
Quantity Relationships
in Chemical Reactions
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
Section 10.4
Limiting Reactants:
The Problem
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
Three atoms of carbon and two molecules of oxygen
react until one is used up.
How many carbon dioxide molecules will result?
The reaction will stop when two molecules of oxygen
are used up. Two carbon dioxide molecules form.
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
Limiting reactant:
The reactant that is completely
used up by the reaction
(oxygen)
Excess reactant:
The reactant initially present in excess,
relative to the limiting reactant
(carbon)
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
Section 10.5
Limiting Reactants:
Comparison-of-Moles
Method
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
Goal 4
Given a chemical equation, or information
from which it may be determined, and initial
quantities of two or more reactants, (a)
identify the limiting reactant, (b) calculate the
theoretical yield of a specified product,
assuming complete use of the limiting
reactant, and (c) calculate the quantity of
reactant initially in excess that remains
unreacted.
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
Comparison-of-Moles Method
How to Solve a Limiting Reactant Problem
1. Convert the number of grams of
each reactant to moles
2. Identify the limiting reactant.
3. Calculate the number of moles of each
species that reacts or is produced.
4. Calculate the number of moles of each
species that remains after the reaction.
5. Change the number of moles of
each species to grams.
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
Example:
A 24.0-g piece of solid sodium is
added to 24.0 g of liquid water.
How many grams of hydrogen will be produced?
How many grams of which reactant will be left over?
2 Na
+ 2H2O
H2
+ 2NaOH
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
2 Na
Grams
at start
+ 2 H2O
H2
+ 2 NaOH
24.0
24.0
0
0
Molar mass, 22.99
g/mol
18.02
2.016
40.00
1.33
0
0
Moles
at start
1.04
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
2 Na
Moles
at start
1.04
Moles used,
– 1.04
produced
+ 2 H2O
H2
+ 2 NaOH
1.33
0
0
– 1.04
+ 0.52
+ 1.04
Moles
at end
0
0.29
0.52
1.04
Grams
at end
0
5.2
1.0
41.6
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
2 Na
Grams
at end
0
+ 2 H2O
5.2
H2
+ 2 NaOH
1.0
41.6
A 24.0-g piece of solid sodium is
added to 24.0 g of liquid water.
How many grams of hydrogen will be produced?
How many grams of which reactant will be left over?
1.0 gram of hydrogen is produced;
5.2 grams of water is left over
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
Section 10.6
Limiting Reactants:
Smaller-Amount
Method
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
Goal 4
Given a chemical equation, or information
from which it may be determined, and initial
quantities of two or more reactants, (a)
identify the limiting reactant, (b) calculate the
theoretical yield of a specified product,
assuming complete use of the limiting
reactant, and (c) calculate the quantity of
reactant initially in excess that remains
unreacted.
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
Smaller-Amount Method
How to Solve a Limiting Reactant Problem
1. Calculate the amount of product that can be
formed by the initial amount of each reactant.
a) The reactant that yields the smaller
amount of product is the limiting reactant.
b) The smaller amount of product is the
amount that will be formed when all of
the limiting reactant is used up.
2. Calculate the amount of excess reactant that is
used by the total amount of limiting reactant.
3. Subtract from the amount of excess reactant present
initially the amount that is used by all of the limiting
reactant. The difference is the amount of excess reactant
that is left.
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
Example:
A 24.0-g piece of solid sodium is
added to 24.0 g of liquid water.
How many grams of hydrogen will be produced?
How many grams of which reactant will be left over?
2 Na
+ 2H2O
H2
+ 2NaOH
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
GIVEN: 24.0 g Na
2 Na
+ 2 HOH
24.0 g Na
1 mol H2
2 mol Na
WANTED: g H2
H2
+ 2 NaOH
1 mol Na
X
22.99 g Na
X
2.016 g H2
mol H2
X
= 1.05 g H2
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
GIVEN: 24.0 g H2O
2 Na
H2
+ 2 HOH
24.0 g H2O
1 mol H2
2 mol H2O
WANTED: g H2
+ 2 NaOH
1 mol H2O
18.02 g H2O
X
X
2.016 g H2
mol H2
X
= 1.34 g H2
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
24.0 g Na and unlimited H2O
produces 1.05 g H2
24.0 g H2O and unlimited Na
produces 1.34 g H2
Therefore 1.05 g H2 is produced
and Na is the limiting reactant
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
How much of the excess reactant, H2O,
is consumed by the reaction of 24.0 g Na?
GIVEN: 24.0 g Na
2 Na
WANTED: g H2O
+ 2 HOH
24.0 g Na X
H2
1 mol Na
22.99 g Na
18.02 g H2O
mol H2O
+ 2 NaOH
X
2 mol H2O
2 mol Na
X
= 18.8 g H2O
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.
How much of the excess reactant, H2O,
remains when the reaction is complete?
24.0 g H2O initially
– 18.8 g H2O reacted
5.2 g H2O remains
Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.