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Mole Relationships in Chemical Equations

Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin CummingsEdited by bbg

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Law of Conservation of Mass

The Law of Conservation of MassLaw 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.

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Conservation of Mass

+

Reactants Products2 moles Ag + 1 moles S = 1 mole Ag2S2 (107.9 g) + 1(32.1 g) = 1 (247.9 g)

247.9247.9 = = 247.9 g247.9 g

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Consider the following equation:4Fe(s) + 3O2(g) 2Fe2O3(s)

This equation can be read in “moles” by placing theword “moles”“moles” between each coefficient and formula.

4 moles4 moles Fe + 3 moles3 moles O2 2 moles2 moles Fe2O3

Reading Equations with Moles

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A mole-mole factor is a ratio of the moles for any two substances in an equation.

4Fe(4Fe(ss) + 3O) + 3O22((gg) 2Fe) 2Fe22OO33((ss))

Fe and OFe and O22 4 moles Fe and 3 moles O2

3 moles O2 4 moles Fe

Fe and FeFe and Fe22OO33 4 moles Fe and 2 moles Fe2O3

2 moles Fe2O3 4 moles Fe

OO22 and Fe and Fe22OO33 3 moles O2 and 2 moles Fe2O3

2 moles Fe2O3 3 moles O2

Writing Mole-Mole Factors

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Consider the following equation:

3 H2(g) + N2(g) 2 NH3(g)

A. A mole-mole factor for H2 and N2 is

1) 3 moles N2 2) 1 mole N2 3) 1 mole N2

1 mole H2 3 moles H2 2 moles H2

B. A mole-mole factor for NH3 and H2 is

1) 1 mole H2 2) 2 moles NH3 3) 3 moles N2

2 moles NH3 3 moles H2 2 moles NH3

Learning Check

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3H3H22((gg) + N) + N22((gg) 2NH) 2NH33((gg))

A. A mole-mole factor for H2 and N2 is 2)2) 1 mole N1 mole N22

3 moles H3 moles H22

B. A mole-mole factor for NH3 and H2 is

2) 2) 2 moles NH2 moles NH33

3 moles H3 moles H22

Solution

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How many moles of Fe2O3 can be produced from

6.0 moles O2?

4Fe(s) + 3O2(g) 2Fe2O3(s)

Relationship: 3 mole O2 = 2 mole Fe2O3

Write a mole-mole factor to determine the moles of Fe2O3.

6.0 mole O2 x 2 mole Fe2O3 = 4.0 moles Fe2O3

3 mole O2

Calculations with Mole Factors

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Guide to Using Mole Factors

Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

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How many moles of Fe are needed for the reaction

of 12.0 moles O2?

4Fe(s) + 3O2(g) 2 Fe2O3(s)

1) 3.00 moles Fe 2) 9.00 moles Fe3) 16.0 moles Fe

Learning Check

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3) 16.0 moles Fe

12.0 moles O2 x 4 moles Fe = 16.0 moles Fe16.0 moles Fe 3 moles O2

Solution