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Chemical Quantities
Chapter 9
Copyright©2004 by Houghton Mifflin Company.
All rights reserved.
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9.1 Information Given by the
Chemical Equation

Balanced equation provides the
relationship between the relative numbers
of reacting molecules and product
molecules
2 CO + O2 →2 CO2
2 CO molecules react with 1 O2 molecules
to produce 2 CO2 molecules
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9.2 Mole-Mole Relationship

Since the information given is relative:
2 CO + O2 →2 CO2
200 CO molec. react with 100 O2 molec. to produce
200 CO2 molec.
2 billion CO molec. react with 1 billion O2 molec. to
produce 2 billion CO2 molec.
2 moles CO molec. react with 1 mole O2 molec. to
produce 2 moles CO2 molec.
12 moles CO molec. react with 6 moles O2 molec.
to produce 12 moles CO2 molec.
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9.3 Mass Calculations

The coefficients in the balanced chemical
equation shows the molecules & mole
ratio of the reactants and products

Since moles can be converted to masses,
we can determine the mass ratio of the
reactants & products as well
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9.3 Mass Calculations
2 CO + O2 →2 CO2
2 moles CO = 1mole O2 = 2 moles CO2
Since 1 mole of CO = 28.01 g, 1 mole O2 = 32.00
g, and 1 mole CO2 = 44.01 g
2(28.01) g CO = 1(32.00) g O2 = 2(44.01) g CO2
56.02 g CO = 32.00 g O2 = 88.02 g CO2
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9.3 Mass Calculations
Determine the number of moles of carbon monoxide
required to react with 3.2 moles oxygen, &
determine the moles of carbon dioxide produced
2 CO + O2 →2 CO2
2 moles CO = 1 mol O2 = 2 moles CO2
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9.3 Mass Calculations
Determine the number of grams of carbon
monoxide required to react with 48.0 g oxygen, &
determine the mass of carbon dioxide produced
2 CO + O2 →2 CO2
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9.3 Mass Calculations
Steps for Calculating the Masses of Reactants &
Products in Chemical Rxns
STEP 1
Balance the equation for the rxn
STEP 2
Convert the masses of reactants or products
to moles using molar mass
STEP 3
Use the balanced equation to set up the
appropriate mole ratios
STEP 4
Use the mole ratios from the balanced
equation to calculate the number of
moles of desired reactant or product
STEP 5
Convert from moles back to masses with
molar mass
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9.4 Limiting & Excess Reactants

When more than 1 reactant is needed in a
rxn, one is usually consumed first

Limiting reactant: a reactant which is
completely consumed in a rxn

Excess reactant: A reactant which is not
completely consumed in a rxn
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9.4 Limiting & Excess Reactants
Determine the number of moles of carbon dioxide
produced when 3.2 moles oxygen reacts with
4.0 moles of carbon monoxide
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9.4 Limiting & Excess Reactants
Determine the number of moles of oxygen are left
over after all of the 4.0 moles of carbon monoxide
has reacted
2 CO + O2 → 2 CO2
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9.4 Limiting & Excess Reactants
Determine the mass of carbon dioxide produced
when 48.0 g of oxygen reacts with 56.0 g of
carbon monoxide
2 CO + O2 →2 CO2
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9.4 Limiting & Excess Reactants
Determine the mass of oxygen left over after 56.0
g of carbon monoxide have reacted
2 CO + O2 →2 CO2
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9.5 Percent Yield




Most reactions do not go to completion
The amount of product made in an experiment is
called the actual yield
The percentage of the theoretical yield that is
actually made is called the percent yield
Theoretical yield: the maximum amount of
product that can be made when the limiting
reactant is completely consumed in a rxn
Percent yield =
Actual yield
x 100%
Theoretical yield
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9.5 Percent Yield
Determine the mass of carbon dioxide produced when
48.0 g of oxygen reacts with 56.0 g of carbon
monoxide. If 72.0 g of carbon dioxide is actually
made, what is the percentage yield
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9.5 Percent Yield
Ammonia and carbon dioxide can react to form urea,
CN2 H4O, and water. If 100.0 g of each reactant results
in the formation of 120.0 g of urea, what is the percent
yield?
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9.5 Percent Yield
Sodium thiosulfate pentahydrate, Na2 S 2 O 3•5H2O, is
produced in a synthesis reaction of elemental sulfur,
S8, sodium sulfite and water. If 3.25 g of sulfur is
boiled with 13.1 g of sodium sulfite and 5.26 g of the
product is collected, what is the percent yield?
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