1 Mass Calculations for Reactions Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings edited by bbg.

1

Mass Calculations for Reactions

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

2

Moles to Grams

Suppose we want to determine the mass (g) of NH3

that can form from 2.50 moles N2.

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

The plan needed would be

moles N2 moles NH3 grams NH3

The factors needed would be:

mole factor NH3/N2 and the molar mass NH3

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Moles to Grams

The setup for the solution would be:

2.50 mole N2 x 2 moles NH3 x 17.0 g NH3

1 mole N2 1 mole NH3

given mole-mole factor molar mass

= 85.0 g NH= 85.0 g NH33

4

How many grams of O2 are needed to produce 0.400 mole Fe2O3 in the following reaction?

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

1) 38.4 g O2

2) 19.2 g O2

3) 1.90 g O2

Learning Check

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2) 19.2 g O2) 19.2 g O22

0.400 mole Fe2O3 x 3 mole O2 x 32.0 g O2= 19.2 g O19.2 g O22

2 mole Fe2O3 1 mole O2

mole factor molar mass

Solution

6

The reaction between H2 and O2 produces 13.1 g water.

How many grams of O2 reacted?

2H2(g) + O2(g) 2H2O(g) ? g 13.1 g

The plan and factors would be

g H2O mole H2O mole O2 g O2

molar mole-mole molar

mass H2O factor mass O2

Calculating the Mass of a Reactant

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The setup would be:

13.1 g H2O x 1 mole H2O x 1 mole O2 x 32.0 g O2

18.0 g H2O 2 moles H2O 1 mole O2

molar mole-mole molar

mass H2O factor mass O2

= 11.6 g O11.6 g O22

Calculating the Mass of a Reactant

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Learning Check

Acetylene gas C2H2 burns in the oxyacetylene torch for welding. How many grams of C2H2 are burned if the reaction produces 75.0 g CO2?

2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(g)

1) 88.6 g C2H2

2) 44.3 g C2H2

3) 22.2 g C2H2

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3) 22.2 g C3) 22.2 g C22HH22

2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(g)

75.0 g CO2 x 1 mole CO2 x 2 moles C2H2 x 26.0 g C2H2

44.0 g CO2 4 moles CO2 1 mole C2H2

molar mole-mole molar

mass CO2 factor mass C2H2

= 22.2 g C= 22.2 g C22HH22

Solution

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Calculating the Mass of Product

When 18.6 g ethane gas C2H6 burns in oxygen, how

many grams of CO2 are produced?

2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g) 18.6 g ? g

The plan and factors would be

g C2H6 mole C2H6 mole CO2 g CO2

molar mole-mole molar mass C2H6 factor mass CO2

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Calculating the Mass of Product

The setup would be

18.6 g C2H6 x 1 mole C2H6 x 4 moles CO2 x 44.0 g CO2

30.1 g C2H6 2 moles C2H6 1 mole CO2

molar mole-mole molarmolar mole-mole molar

mass Cmass C22HH66 factor mass CO factor mass CO22

= 54.4 g CO54.4 g CO22

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Learning Check

How many grams H2O are produced when 35.8 g C3H8 react by the following equation?

C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)

1. 14.6 g H2O

2. 58.4 g H2O

3. 117 g H2O

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Solution

C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)

35.8 g C3H8x 1 mole C3H8 x 4 mole H2O x 18.0 g H2O

44.1 g C3H8 1 mole C3H8 1 mole H2O

molar mole-mole molar mass C3H8 factor mass H2O

= 58.4 g H58.4 g H22O (2)O (2)