Chapter 5 An Introduction to Chemical Reactions

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Chapter 5 An Introduction to Chemical Reactions

Review Skills 5.1 Chemical Reactions and Chemical Equations

? Interpreting a Chemical Equation ? Balancing Chemical Equations

Internet: Balancing Equations Tutorial 5.2 Solubility of Ionic Compounds and Precipitation Reactions

? Water Solutions of Ionic Compounds Internet: Dissolving NaCl

? Precipitation Reactions Internet: Precipitation Reaction

? Predicting Water Solubility Internet: Predicting Water Solubility Internet: Writing Net Ionic Equations for Precipitation Reactions Special Topic 5.1: Hard Water and Your Hot Water Pipes

Having Trouble? Chapter Glossary

Internet: Glossary Quiz Chapter Objectives Review Questions Key Ideas Chapter Problems

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Study Guide for An Introduction to Chemistry

Section Goals and Introductions

Now that you know about atoms, elements, chemical bonds, and chemical compounds, you are ready to be introduced to chemical changes and the ways that we describe them.

Section 5.1 Chemical Reactions and Chemical Equations Goals ? To describe the nature of chemical reactions. ? To show how chemical reactions can be described with chemical equations. ? To show how to balance chemical equations. This section starts with a brief description of chemical reactions. The introduction to chemical reactions is followed by a description of how chemical changes are described with chemical equations. You will see many chemical equations in this text, so it is very important that you be able to interpret them. Sample Study Sheet 5.1: Balancing Chemical Equations describes the important skill of balancing equations so that they reflect the fact that the number of atoms of each element for the products of chemical changes always equals the number of atoms of each element in the initial reactants. Our Web site provides a tutorial that will allow you to practice balancing chemical equations.

Internet: Balancing Equations Tutorial

Section 5.2 Solubility of Ionic Compounds and Precipitation Reactions Goals ? To describe the process by which ionic compounds dissolve in water. ? To describe the changes that take place on the molecular level during precipitation reactions. ? To provide guidelines for predicting water solubility of ionic compounds. ? To describe the process for predicting precipitation reactions and writing chemical equations for them. This section begins by describing solutions in general, describing solutions of ionic compounds in particular, and most important, describing the process by which ionic compounds dissolve in water. If you develop the ability to see this process in your mind's eye, it will help you understand the process of chemical changes between substances in solution. An animation on our Web site will help you to visualize the process of dissolving sodium chloride in water.

Internet: Dissolving NaCl

The definition of the nature of solutions leads to the description of a simple chemical change that takes place when two solutions of ionic compounds are mixed, which leads to the formation of an ionic compound that is insoluble in water and therefore comes out of solution as a solid. You will learn how to visualize the changes that take place in this type of reaction (called a precipitation reaction), how to predict whether mixtures of two solutions of ionic compounds will lead to a precipitation reaction, and how to write chemical equations for those reactions that do take place. Our Web site provides (1) an animation that will help you to visualize precipitation reactions, (2) a tutorial that will allow you to practice predicting

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whether ionic compounds are soluble in water or not, and (3) a description of the process for writing complete ionic and net ionic equations.

Internet: Precipitation Reactions Internet: Predicting Water Solubility Internet: Writing Net Ionic Equations for Precipitation Reactions You might want to look closely at the Having Trouble section at the end of Chapter 5. It describes all of the skills from Chapters 3-5 that are necessary for writing chemical equations for precipitation reactions. Students often have trouble with writing these equations, not because of the new components to the process found in Chapter 5, but because they are still having trouble with skills from Chapters 3 and 4.

Chapter 5 Map

Chapter Checklist

Read the Review Skills section. If there is any skill mentioned that you have not yet mastered, review the material on that topic before reading this chapter. Read the chapter quickly before the lecture that describes it. Attend class meetings, take notes, and participate in class discussions. Work the Chapter Exercises, perhaps using the Chapter Examples as guides. Study the Chapter Glossary and test yourself at our Web site: Internet: Glossary Quiz

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Study Guide for An Introduction to Chemistry

Study all of the Chapter Objectives. You might want to write a description of how you will meet each objective. (Although it is best to master all of the objectives, the following objectives are especially important because they pertain to skills that you will need while studying other chapters of this text: 3, 4, and 10.) Reread the Study Sheets in this chapter and decide whether you will use them or some variation on them to complete the tasks they describe.

Sample Study Sheet 5.1: Balancing Chemical Equations

Sample Study Sheet 5.2: Predicting Precipitation Reactions and Writing Precipitation Equations

Memorize the following solubility guidelines. Be sure to check with your instructor to determine how much you are expected to know of the following guidelines.

Category Soluble cations

Soluble anions

Ions

Group 1 metallic ions and ammonium, NH4+

NO3? and C2H3O2?

Usually soluble Cl?, Br?, and I?

anions

SO42-

usually

CO32?, PO43?, and OH?

insoluble anions

Except with these ions

Examples

No exceptions

Na2CO3, LiOH, and (NH4)2S are soluble.

No exceptions

Bi(NO3)3, and Co(C2H3O2)2 are soluble.

Soluble with some

exceptions, including with Ag+ and Pb2+

CuCl2 is water soluble, but AgCl is insoluble.

Soluble with some

exceptions, including with Ba2+ and Pb2+

FeSO4 is water soluble, but BaSO4 is insoluble.

Insoluble with some

exceptions, including with group 1 elements and NH4+

CaCO3, Ca3(PO4)2, and Mn(OH)2 are insoluble in water, but (NH4)2CO3, Li3PO4, and CsOH are soluble.

To get a review of the most important topics in the chapter, fill in the blanks in the Key Ideas section. Work all of the selected problems at the end of the chapter, and check your answers with the solutions provided in this chapter of the study guide. Ask for help if you need it.

Web Resources

Internet: Balancing Equations Internet: Dissolving NaCl Internet: Precipitation Reaction Internet: Predicting Water Solubility Internet: Writing Complete and Net-Ionic Equations for Precipitation Reactions Internet: Glossary Quiz

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Exercises Key

Exercise 5.1 - Balancing Equations: Balance the following chemical

equations. (Obj 4) a. P4(s) + 6Cl2(g) 4PCl3(l) b. 3PbO(s) + 2NH3(g) 3Pb(s) + N2(g) + 3H2O(l) c. P4O10(s) + 6H2O(l) 4H3PO4(aq) d. 3Mn(s) + 2CrCl3(aq) 3MnCl2(aq) + 2Cr(s) e. C2H2(g) + 5/2O2(g) 2CO2(g) + H2O(l) or 2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(l) f. 3Co(NO3)2(aq) + 2Na3PO4(aq) Co3(PO4)2(s) + 6NaNO3(aq) g. 2CH3NH2(g) + 9/2O2(g) 2CO2(g) + 5H2O(l) + N2(g) or 4CH3NH2(g) + 9O2(g) 4CO2(g) + 10H2O(l) + 2N2(g) h. 2FeS(s) + 9/2O2(g) + 2H2O(l) Fe2O3(s) + 2H2SO4(aq) or 4FeS(s) + 9O2(g) + 4H2O(l) 2Fe2O3(s) + 4H2SO4(aq)

Exercise 5.2 - Predict ing Wat er Solubilit y: Predict whether each of the

following is soluble or insoluble in water. (Obj 9) a. Hg(NO3)2 (used to manufacture felt) soluble b. BaCO3 (used to make radiation-resistant glass for color TV tubes) insoluble c. K3PO4 (used to make liquid soaps) soluble d. PbCl2 (used to make other lead salts) insoluble e. Cd(OH)2 (storage battery electrodes) insoluble

Exercise 5.3 - Precipit at ion React ions: Predict whether a precipitate will

form when each of the following pairs of water solutions is mixed. If there is a precipitation reaction, write the complete equation that describes the reaction. (Obj 10)

a. 3CaCl2(aq) + 2Na3PO4(aq) Ca3(PO4)2(s) + 6NaCl(aq) b. 3KOH(aq) + Fe(NO3)3(aq) 3KNO3(aq) + Fe(OH)3(s) c. NaC2H3O2(aq) + CaSO4(aq) No Reaction d. K2SO4(aq) + Pb(NO3)2(aq) 2KNO3(aq) + PbSO4(s)

Review Questions Key

1. Write the formulas for all of the diatomic elements. H2, N2, O2, F2, Cl2, Br2, I2

2. Predict whether atoms of each of the following pairs of elements would be expected to form ionic or covalent bonds.

a. Mg and F ionic

c. Fe and O ionic

b. O and H covalent

d. N and Cl covalent

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