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1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc.

1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Page 1: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

1

Chapter 5 Chemical Quantities and Reactions

5.4 Chemical Equations

Copyright © 2009 by Pearson Education, Inc.

Page 2: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

2

Chemical Equations

A chemical equation gives• the formulas of the reactants on the left of the arrow.• the formulas of the products on the right of the arrow.

Reactants Product

C(s)

O2 (g)CO2 (g)

Copyright © 2009 by Pearson Education, Inc.

Page 3: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

3

Symbols Used in Equations

Symbols in chemical equations show

• the states of the reactants.

• the states of the products.

• the reaction conditions.

TABLE

Page 4: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Chemical Equations are Balanced

In a balancedchemical reaction• no atoms are

lost or gained.

• the number of reacting atoms is equal to the number of product atoms.

Copyright © 2009 by Pearson Education, Inc.

Page 5: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

5

A Balanced Chemical Equation

In a balanced chemical equation,• the number of each type of atom on the reactant side is

equal to the number of each type of atom on the product side.

• numbers called coefficients are used in front of one or more formulas to balance the number of atoms.

Al + S Al2S3 Not Balanced

2Al + 3S Al2S3 Balanced using coefficients

2 Al = 2 Al Equal number of Al atoms 3 S = 3 S Equal number of S atoms

Page 6: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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A Study Tip: Using Coefficients

When balancing a chemical equation, • use one or more coefficients to balance atoms.• never change the subscripts of any formula.

N2 + O2 NO Not Balanced

N2 + O2 N2O2 Incorrect formula

N2 + O2 2NO Correctly balanced

using coefficients

Page 7: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Learning Check

State the number of atoms of each element on thereactant side and the product side for each of thefollowing balanced equations.

A. P4(s) + 6Br2(l) 4PBr3(g)

B. 2Al(s) + Fe2O3(s) 2Fe(s) + Al2O3(s)

Page 8: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Solution

A. P4(s) + 6Br2(l) 4PBr3(g)

4 P atoms = 4 P atoms

12 Br atoms = 12 Br atoms

B. 2Al(s) + Fe2O3(s) 2Fe(s) + Al2O3(s)

2 Al atoms = 2 Al atoms

2 Fe atoms = 2 Fe atoms

3 O atoms = 3 O atoms

Page 9: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Learning Check

Determine if each equation is balanced or not.

A. Na(s) + N2(g) Na3N(s)

B. C2H4(g) + H2O(l) C2H6O(l)

Page 10: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Solution

Determine if each equation is balanced or not.

A. Na(s) + N2(g) Na3N(s) No. 2 N atoms on reactant side; only 1 N atom

on the product side. 1 Na atom on reactant side; 3 Na atoms on the product side.

B. C2H4(g) + H2O(l) C2H6O(l) Yes. 2 C atoms = 2 C atoms 6 H atoms = 6 H atoms

1 O atom = 1 O atom

Page 11: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Guide to Balancing a Chemical Equation

Page 12: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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To balance the following equation, Fe3O4(s) + H2(g) Fe(s) + H2O(l)

• work on one element at a time.• use only coefficients in front of formulas.• do not change any subscripts.Fe: Fe3O4(s) + H2(g) 3Fe(s) + H2O(l)

O: Fe3O4(s) + H2(g) 3Fe(s) + 4H2O(l)

H: Fe3O4(s) + 4H2(g) 3Fe(s) +

4H2O(l)

Steps in Balancing an Equation

Page 13: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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1. Write the equation with the correct formulas. NH3(g) + O2(g) NO(g) + H2O(g)

2. Determine if the equation is balanced.No, H atoms are not balanced.

3. Balance with coefficients in front of formulas. 2NH3(g) + O2(g) 2NO(g) + 3H2O(g)

Double the coefficients to give even number of O atoms.4NH3(g) + 7O2(g) 4NO(g) + 6H2O(g)

Balancing Chemical Equations

Page 14: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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4. Check that atoms of each element are equal in reactants and products.

4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)

4 N (4 x 1 N) = 4 N (4 x 1 N) 12 H (4 x 3 H) = 12 H (6 x 2 H) 10 O (5 x 2 O) = 10 O (4 O + 6 O)

Balancing Chemical Equations

Page 15: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Equation for a Chemical Reaction

Copyright © 2009 by Pearson Education, Inc.

Page 16: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Checking a Balanced Equation

Reactants Products 1 C atom = 1 C atom 4 H atoms = 4 H atoms 4 O atoms = 4 O atoms

Copyright © 2009 by Pearson Education, Inc.

Page 17: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Check the balance of atoms in the following:

Fe3O4(s) + 4H2(g) 3Fe(s) + 4H2O(l)

A. Number of H atoms in products.

1) 2 2) 4 3) 8

B. Number of O atoms in reactants.

1) 2 2) 4 3) 8

C. Number of Fe atoms in reactants.

1) 1 2) 3 3) 4

Learning Check

Page 18: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Fe3O4(s) + 4H2(g) 3Fe(s) + 4H2O(l)

A. Number of H atoms in products. 3) 8 (4H2O)

B. Number of O atoms in reactants. 2) 4 (Fe3O4)

C. Number of Fe atoms in reactants. 2) 3 (Fe3O4)

Solution

Page 19: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Balance each equation and list the coefficients in the balanced equation going from reactants to products:

A. __Mg(s) + __N2(g) __Mg3N2(s)

1) 1, 3, 2 2) 3, 1, 2 3) 3, 1, 1

B. __Al(s) + __Cl2(g) __AlCl3(s)

1) 3, 3, 2 2) 1, 3, 1 3) 2, 3, 2

Learning Check

Page 20: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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A. 3) 3, 1, 1 3Mg(s) + 1N2(g) 1Mg3N2(s)

B. 3) 2, 3, 2

2Al(s) + 3Cl2(g) 2AlCl3(s)

Solution

Page 21: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Equations with Polyatomic Ions

2Na3PO4(aq) + 3MgCl2 (aq) Mg3 ( PO4(s) + 6NaCl(aq)

Copyright © 2009 by Pearson Education, Inc.

Page 22: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Balancing with Polyatomic Ions

Na3PO4(aq) + MgCl2(aq) Mg3(PO4)2(s) + NaCl(aq)

Balance PO43- as a unit

2Na3PO4(aq) + MgCl2(aq) Mg3(PO4)2(s) + NaCl(aq) 2 PO4

3- = 2 PO43-

Check Na + balance 6 Na+ = 6 Na+

Balance Mg and Cl2Na3PO4(aq) + 3MgCl2(aq) Mg3(PO4)2(s) + 6NaCl(aq)

3 Mg2+ = 3 Mg2+

6 Cl- = 6 Cl-

Page 23: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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Balance and list the coefficients from reactants to products.

A. __Fe2O3(s) + __C(s) __Fe(s) + __CO2(g)

1) 2, 3, 2, 3 2) 2, 3, 4, 3 3) 1, 1, 2, 3

B. __Al(s) + __FeO(s) __Fe(s) + __Al2O3(s)

1) 2, 3, 3, 1 2) 2, 1, 1, 1 3) 3, 3, 3, 1

C. __Al(s) + __H2SO4(aq) __Al2(SO4)3(aq) + __H2(g)

1) 3, 2, 1, 2 2) 2, 3, 1, 3 3) 2, 3, 2, 3

Learning Check

Page 24: 1 Chapter 5 Chemical Quantities and Reactions 5.4 Chemical Equations Copyright © 2009 by Pearson Education, Inc

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A. 2) 2, 3, 4, 3

2Fe2O3(s) + 3C(s) 4Fe(s) + 3CO2(g)

B. 1) 2, 3, 3, 1

2Al(s) + 3FeO(s) 3Fe(s) + 1Al2O3(s)

C. 2) 2, 3, 1, 3 2Al(s) + 3H2SO4(aq) 1Al2(SO4)3(aq) + 3H2(g)

Solution