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Chapter 9 Lecture
Basic Chemistry
Fifth Edition
Chapter 9 Chemical Quantities
in Reactions
9.1 Conservation
of Mass
Conservation of Mass
The law of conservation of mass indicates that
in an ordinary chemical reaction
• matter cannot be created or destroyed
• no change in total mass occurs in a reaction
• mass of products is equal to mass of reactants
Learning Goal Calculate the total mass of reactants
and the total mass of products in a balanced chemical
equation.
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Information from a Balanced
Equation
Conservation of Mass
Reactants
2 mol of Ag + 1 mol of S
2 (107.9 g) + 1(32.1 g)
247.9
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=
=
Products
1 mol of Ag2S
1 (247.9 g)
=
247.9 g
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Basic Chemistry
Chapter 9 Lecture
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
Reading an Equation in
Moles
Fifth Edition
Chapter 9 Chemical Quantities
in Reactions
9.2 Calculating Moles
Using Mole–Mole
Factors
Learning Goal Use a mole–mole factor from a balanced
chemical equation to calculate the number of moles of
another substance in the reaction.
Consider the following equation:
2Fe(s) + 3S(s)
Fe2S3(s)
An equation can be read in moles by placing the
words “mol of” between each coefficient and
formula.
2 mol of Fe + 3 mol of S
1 mol of Fe2S3
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Writing Mole-Mole Factors
Learning Check
A mole-mole factor is a ratio of the moles for two
Consider the following equation:
3H2(g) + N2(g)
2NH3(g)
substances in an equation.
2Fe(s)
+
Fe and S
Fe and Fe2S3
S and Fe2S3
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3S(s)
Fe2S3(s)
2 mol Fe
and 3 mol S
3 mol S
2 mol Fe
2 mol Fe
and 1 mol Fe2S3
1 mol Fe2S3
2 mol Fe
3 mol S
and 1 mol Fe2S3
1 mol Fe2S3
3 mol S
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Using Mole-Mole Factors
A. A mole factor for H2 and N2 is
1) 3 mol N2
2) 1 mol N2
1 mol H2
3 mol H2
3) 1 mol N2
2 mol H2
B. A mole factor for NH3 and H2 is
1) 1 mol H2
2) 2 mol NH3
2 mol NH3
3 mol H2
3) 3 mol N2
2 mol NH3
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Basic Chemistry
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Calculations with Mole
Factors
How many moles of Fe are needed for the reaction of
12.0 mol of O2?
4Fe(s) + 3O2(g)
2Fe2O3(s)
1) 3.00 mol of Fe
2) 9.00 mol of Fe
3) 16.0 mol of Fe
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Basic Chemistry
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Calculations with Mole-Mole
Factors
STEP 1 Write the given and needed number of
moles.
Given 12 mol of O2 Need moles of Fe
STEP 2 Write a plan to convert the given to the
needed moles.
mol of O2
mol of Fe
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Basic Chemistry
Calculations with Mole-Mole
Factors (continued)
STEP 3 Use coefficients to write relationship and
mole-mole factors.
4 mol of Fe = 3 mol of O2
4 mol Fe and 3 mol O2
3 mol O2
4 mol Fe
STEP 4 Set up problem using the molemole
factor that cancels given moles.
12.0 mol O2 x
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4 mol Fe = 16.0 mol Fe (C)
3 mol O2
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4/25/2017
Chapter 9 Lecture
Basic Chemistry
Calculating the Masses of
Reactants and Products
Fifth Edition
Chapter 9 Chemical
Quantities in Reactions
9.3 Mass Calculations
for Reactions
Learning Goal Given the mass in grams of a
substance in a reaction, calculate the mass in
grams of another substance in the reaction.
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Basic Chemistry
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Example of Converting Moles
to Grams of Product
Suppose we want to determine the mass (g) of NH 3
that can form from 2.50 mol of N 2.
N2(g) + 3H2(g)
2NH3(g)
STEP 1 Use molar mass to convert grams of given
to moles (if necessary).
Given 2.50 mol of N2 Need grams of NH3
STEP 2 Write a mole-mole factor from the
coefficients in the equation.
1 mol of N2 = 2 mol of NH3
1 mol N2 and 2 mol NH3
2 mol NH3
1 mol N2
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STEP 3 Convert moles of given to moles of
needed substance using the mole-mole factor.
2.50 mol N2 x 2 mol NH3 = 5.00 mol of NH3
1 mol N2
STEP 4 Convert moles of needed substances to
grams using molar mass.
1 mol of NH3 = 17.0 g of NH3
1 mol NH3 and 17.0 g NH3
17.0 g NH3
1 mol NH3
5.00 mol NH3 x 17.0 g NH3 = 85.0 g of NH3
1 mol NH3
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Basic Chemistry
Acetylene gas C2H2 burns in the oxyacetylene torch
for welding. How many grams of C 2H2 are burned if
the reaction produces 75.0 g of CO 2?
4CO2(g) + 2H2O(g)
1) 88.4 g C2H2
2) 44.2 g C2H2
3) 22.1 g C2H2
The fuel heptane (C7H16) is designated as
the zero point in the octane rating of
gasoline. Heptane is an undesirable
compound in gasoline because it burns
rapidly and causes engine knocking. How
many grams of O2 are required to react with
22.5 g of C7H16?
C7H16(l) + 11O2(g)
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Grams of Reactant from
Grams of Reactant
Learning Check
2C2H2(g) + 5O2(g)
Converting Moles to
Grams (continued)
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Basic Chemistry

7CO2(g) + 8H2O(g)
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Grams of Reactant from Grams
of Reactant
STEP 1 State the given and needed quantities (grams).
Mass of Reactant from Mass of
Reactant
STEP 3 Use coefficients to write mole−mole factors;
write molar masses.
STEP 2 Write a plan to convert the given to the needed
quantity (grams).
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
Mass of Reactant from Mass of
Reactant
STEP 4 Set up the problem to give the needed quantity
(grams).
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Basic Chemistry
Learning Check
How many grams of potassium are
required to produce 36.0 g of KCl?
2K(s) + Cl2(g)
2KCl(s)
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Basic Chemistry
Practice
Practice:
•
•
How many grams of ammonia are
produced from the decomposition of
1.00 x 103 grams of ammonium
carbonate?
Basic Chemistry
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Copyright © 2011 Pearson Education, Inc.
Copyright © 2011 Pearson Education, Inc.
Calculate the number of chlorine
molecules required to react with 10.0
grams of sodium metal.
Basic Chemistry
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Challenge:
•
The complete combustion of octane in
automobiles requires the presence of
molecular oxygen. Octane has a
density of 0.692 g/mL at 20oC. How
many grams of molecular oxygen are
required to burn 1.00 L of Octane?
Basic Chemistry
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