Free Study Guide for
Cracolice • Peters
Introductory Chemistry: An Active Learning Approach
Second Edition
www.brookscole.com/chemistry
Chapter 8
Reactions and Equations
Chapter 8–Assignment A: Balancing Chemical Equations
In Chapter 2 you learned about the characteristics of a chemical change. Chemists describe
chemical changes, or reactions, by writing chemical equations. In this assignment you'll
learn to describe the chemical reactions of elements and compounds by using a chemical
equation.
The main ideas in this assignment are:
1)
A chemical equation is a shorthand description of a chemical reaction.
2)
Chemical equations can be interpreted on a particulate scale or on a molar scale.
3)
A balanced chemical equation reflects the Law of Conservation of Mass.
4)
The subscripts in a chemical equation may never be changed simply to balance the
equation. Changing a subscript in the formula of a substance changes the chemical
identity of that substance (Law of Definite Composition).
5)
When balancing an equation start big and work to small.
Learning Procedures
Study
Sections 8.1–8.3. Focus on Goals 1–2 as you study.
Strategy
Practice. The more equations you balance, the better you get at it. When you
make a mistake, think about why you made that mistake and take action to
change your thinking. Always, always, always check your answers. You will
never misbalance an equation if you check your work.
Answer
The Equation-Balancing Exercises (1–25) and Questions, Exercises, and
Problems 1. Check your answers with those at the end of the chapter.
Workbook
If your instructor recommends the Active Learning Workbook, do
Questions, Exercises, and Problems 1.
46
Copyright © 2004 Brooks/Cole, a division of Thomson Learning, Inc.
No part of this work may be reproduced without the written permission of the publisher.
Chapter 8
Reactions and Equations
Chapter 8–Assignment B: Writing and Balancing Chemical Equations
In the last assignment you got a start on balancing chemical equations, if all the reactants
and products were given to you. In this assignment you'll learn to write the equations
yourself, before balancing them. In addition, you will learn to organize these equations by
types of reactants and products.
The important ideas in this assignment are:
1)
You must know the correct formulas for all the reactants and products before you
can write a chemical equation.
2)
Chemical equations are organized by reaction types.
3)
A combination reaction has the equation type A + X Æ AX.
4)
A decomposition reaction has the equation type AX Æ!A + X.
5)
A complete oxidation or burning reaction has the equation type
Cx Hy Oz + O2 Æ CO2 + H2 O.
6)
A single-replacement oxidation-reduction reaction has the equation type
A + BX Æ AX + B.
7)
A double-replacement precipitation reaction has the equation type
AX + BY Æ AY + BX.
8)
A double-replacement neutralization reaction has the equation type
HX + MOH Æ!HOH + MX.
Learning Procedures
Study
Sections 8.4–8.11. Focus on Goals 3–8 as you study.
Strategy
Table 8.2 provides a summary of all the types of reactions and equations.
As with Assignment A, practice is the key.
Answer
The Equation-Classification Exercises (3–12) and Questions, Exercises, and
Problems 2–14. Check your answers with those at the end of the chapter.
Workbook
If your instructor recommends the Active Learning Workbook, do
Questions, Exercises, and Problems 1.
Chapter 8–Assignment C: Summary and Review
When writing chemical equations, you may encounter several major pitfalls. Fortunately,
they are easily avoided. The most common error is simply not following the three-step
Writing and Balancing a Chemical Equation Procedure given in Section 8.4.
47
Copyright © 2004 Brooks/Cole, a division of Thomson Learning, Inc.
No part of this work may be reproduced without the written permission of the publisher.
Study Guide for Introductory Chemistry: An Active Learning Approach
First, look at the reactants and conditions to classify the reaction. The major reaction types
that do not occur in water are combination, decomposition, and complete oxidation. Don't
forget to add O2 (g) in burning reactions. In water solutions, some reaction types are singlereplacement oxidation-reduction, double-replacement precipitation, and double-replacement
neutralization reactions. Remember, if you can recognize the reaction type, you can predict
the products and write correct formulas for them.
After you have the correct formula for each reactant and product, balance the number of
atoms of each element on each side of the equation by changing coefficients only. Never
change the subscript to balance an equation. A coefficient is not the same as a subscript; 3
Br2 is not the same as Br6 or 6 Br. The formula writing skills you developed in Chapter 6
will serve you well here.
It's easier to balance double replacement equations if you balance groups rather than atoms.
If you see a polyatomic group that's the same on both sides of the equation, balance the
number of that group. For example, if there are sulfate groups on both sides of the arrow,
there must be the same number of sulfates. Don't balance all the S atoms in the sulfates first,
then all the O atoms in the sulfates. That takes much too long. Just balance the sulfates.
In Chapter 6 you learned the formula for water is H2 O. That's true, but in reactions, water
often reacts as if it were HOH. You may find acid-base neutralization equation easier to
balance if you write the water product as HOH. All the H atoms at the front of the water
come from the reactant acid, all the OH comes from the reactant base, and the number of H
equals the number of OH.
You must be able to balance these chemical equations, because in Chapter 9 you must start
with a balanced chemical equation to see how much of a reactant or product is involved in a
reaction.
Learning Procedures
Review
your lecture and textbook notes.
the Chapter in Review and the Key Terms and Concepts, and read the Study
Hints and Pitfalls to Avoid.
Answer
Questions, Exercises, and Problems 15–40. Check your answers with those
at the end of the chapter.
Workbook
If your instructor recommends the Active Learning Workbook, do
Questions, Exercises, and Problems 15–36. Include Questions 37–38 if
assigned by your instructor.
Take
the chapter summary test that follows. Check your answers with those at the
end of this assignment.
48
Copyright © 2004 Brooks/Cole, a division of Thomson Learning, Inc.
No part of this work may be reproduced without the written permission of the publisher.
Chapter 8
Reactions and Equations
Chapter 8 Sample Test
Instructions: For each reaction described, identify the reaction type and write a balanced
chemical equation.
1)
Solid calcium oxide is formed from its elements.
2)
Solid barium oxide and liquid water result from the decomposition of solid barium
hydroxide.
3)
Gaseous C4 H9 CHO is completely oxidized.
4)
Hydrogen gas and a solution of lithium hydroxide are the products of the reaction
between solid lithium metal and liquid water.
5)
Potassium hydroxide solution reacts with a solution of copper(II) nitrate. Copper(II)
hydroxide is a solid product; the other product is aqueous.
6)
Aqueous solutions of hydrobromic acid and sodium hydroxide react.
7)
When chloric acid is poured over solid calcium carbonate, carbon dioxide bubbles
off, leaving water and aqueous calcium chlorate as the other products. (You do not
have to classify this reaction.)
49
Copyright © 2004 Brooks/Cole, a division of Thomson Learning, Inc.
No part of this work may be reproduced without the written permission of the publisher.
Study Guide for Introductory Chemistry: An Active Learning Approach
Answers to Chapter 8 Sample Test
1)
Combination; 2 Ca(s) + O2 (g) Æ 2 CaO(s)
2)
Decomposition; Ba(OH)2 (s) Æ BaO(s) + H2 O(l)
3)
Complete oxidation or burning;
C4 H9 CHO(g) + 7 O2 (g) Æ 5 CO2 (g) + 5 H2 O(g)
4)
Single-replacement oxidation-reduction;
2 Li(s) + 2 H2 O(l) Æ H2 (g) + 2 LiOH(aq)
5)
Double-replacement precipitation;
2 KOH(aq) + Cu(NO3 )2 (aq) Æ Cu(OH)2 (s) + 2 KNO3 (aq)
6)
Double-replacement neutralization;
HBr(aq) + NaOH(aq) Æ H2 O(l) + NaBr(aq)
7)
2 HClO3 (aq) + CaCO3 (s) Æ CO2 (g) + H2 O(l) + Ca(ClO3 )2 (aq)
50
Copyright © 2004 Brooks/Cole, a division of Thomson Learning, Inc.
No part of this work may be reproduced without the written permission of the publisher.