Chapter 9

Chapter 9

Chemical Reactions

National Standards for Chapter 9

• UCP.3 – Change, constancy, and measurement• UCP.5 – Form and function• A.1 –Abilities necessary to do scientific inquiry• A.2 – Understandings about scientific inquiry• B-2 – Structure and properties of matter• B-3 – Chemical reactions• B-6 – Interactions of energy and matter

Vocabulary/Study Guide

• Define each term using the Glossary• Either write on the handout, or use your own

paper• This is due on Test Day (tentatively, Thursday,

March 6)

Section 1: Reactions and Equations

• National Standards:• UCP.3 – Change, constancy, and measurement• UCP.5 – Form and function• A.1 –Abilities necessary to do scientific inquiry• B-2 – Structure and properties of matter• B-3 – Chemical reactions• B-6 – Interactions of energy and matter

Objectives – Section 1

• Recognize evidence of chemical change.• Represent chemical reactions with equations. • Balance chemical equations.

REVIEW VOCABULARY:chemical change: a process involving one or more

substances changing into a new substance

New Vocabulary

chemical reaction

reactant

product

chemical equation

coefficient

Chemical reactions are represented by balanced chemical equations.

Launch Lab

Title: How do you know when a chemical change has occurred? (page 280)

Math Skills Transparency 11

Chemical Reactions

• The process by which one or more substances are rearranged to form different substances is called a chemical reaction.

Chemical Reactions

• Evidence that a chemical reaction may have occurred:– Change in temperature– Change in color– Odor – Gas bubbles– Appearance of a solid (precipitate)

Representing Chemical Reactions

• Chemists use statements called equations to represent chemical reactions.

• Reactants are the starting substances.

• Products are the substances formed in the reaction.

• This table summarizes the symbols used in chemical equations.


• In word equations, aluminum(s) + bromine(l) → aluminum bromide(s) reads as “aluminum and bromine react to produce aluminum bromide”.

• Skeleton equations use symbols and formulas to represent the reactants and products.

Al(s) + Br(l) → AlBr3(s)• Both word and skeleton equations lack information

about how many atoms are involved in the reaction.


• A chemical equation is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.


• Practice Problems #1-3, page 284

Balancing Chemical Equations

• This figure shows the balanced equation for the reaction between aluminum and bromine.


• A coefficient in a chemical equation is the number written in front of a reactant or product, describing the lowest whole-number ratio of the amounts of all the reactants and products.




Transparency 29: Parts of a Balanced Chemical Equation



Transparency 30: Balancing Chemical Equations


• The most fundamental law in chemistry is the law of conservation of mass.

• Balanced equations show this law.


Homework, Section 1

• SECTION 1 REVIEW, Page 288 • Questions #7-13• Answer with complete sentences• Due tomorrow

Section 2: Classifying Chemical Reactions

• National Standards:• UCP.3 – Change, constancy, and measurement• UCP.5 – Form and function• A.1 –Abilities necessary to do scientific inquiry• B-2 – Structure and properties of matter• B-3 – Chemical reactions


• Classify chemical reactions.• Identify the characteristics of different

classes of chemical reactions.

Review Vocabulary:metal: an element that is a solid at room temperature,

a good conductor of heat and electricity, and is generally shiny

New Vocabulary

synthesis reactioncombustion reactiondecomposition reactionsingle-replacement reactiondouble-replacement reactionprecipitate

There are four types of chemical reactions: synthesis, combustion, decomposition, and replacement reactions.

Types of Chemical Reactions

• Chemists classify reactions in order to organize the many types.

Synthesis Reactions• A synthesis reaction is a reaction in which two

or more substances react to produce a single product.

• When two elements react, the reaction is always a synthesis reaction.

Combustion Reactions

• In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light.

• Heated hydrogen reacts with oxygen to produce heat and water in a combustion reaction. This is also a synthesis reaction.

Combustion Reactions


Decomposition Reactions

• A decomposition reaction is one in which a single compound breaks down into two or more elements or new compounds.

• Decomposition reactions often require an energy source, such as heat, light, or electricity, to occur.

Decomposition Reactions


Replacement Reactions

• A reaction in which the atoms of one element replace the atoms of another element in a compound is called a single replacement reaction.

A + BX → AX + B


• A metal will not always replace a metal in a compound dissolved in water because of differing reactivities.

• An activity series can be used to predict if reactions will occur.


• Halogens frequently replace other halogens in replacement reactions.

• Halogens also have different reactivities and do not always replace each other.

Transparency 31: The Activity Series


Title: Analyze Trends, page 294




• Double replacement reactions occur when ions exchange between two compounds.

• This figure shows a generic double replacement equation.


• The solid product produced during a chemical reaction in a solution is called a precipitate.

• All double replacement reactions produce either water, a precipitate, or a gas.


• This table shows the steps to write double replacement reactions.




• This table summarizes different ways to predict the products of a chemical reaction.

Transparency 32: Summary of Reaction Types

Lab: Develop an Activity Series, page 310

Lab: Single-Replacement Reactions

Lab: Double-Replacement Reactions

Homework, Section 2

• SECTION 2 REVIEW, Page 298• Questions #29-34• Answer with complete sentences• Due tomorrow

Section 3: Reactions in Aqueous Solutions

• National Standards:• UCP.3 – Change, constancy, and measurement• UCP.5 – Form and function• A.1 –Abilities necessary to do scientific inquiry• A.2 – Understandings about scientific inquiry• B-2 – Structure and properties of matter• B-3 – Chemical reactions• B-6 – Interactions of energy and matter


• Describe aqueous solutions.• Write complete ionic and net ionic equations

for chemical reactions in aqueous solutions.• Predict whether reactions in aqueous

solutions will produce a precipitate, water, or a gas.

Review Vocabulary:solution: a uniform mixture that might contain solids,

liquids, or gases

New Vocabulary

aqueous solutionsolutesolvent complete ionic equationspectator ionnet ionic equation

Double-replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or gases.

Aqueous Solutions

• An aqueous solution contains one or more dissolved substances (called solutes) in water.

• The solvent is the most plentiful substance in a solution.

Aqueous Solutions

• Water is always the solvent in an aqueous solution.

• There are many possible solutes—sugar and alcohol are molecular compounds that exist as molecules in aqueous solutions.

• Compounds that produce hydrogen ions in aqueous solutions are acids.

Aqueous Solutions

• Ionic compounds can also be solutes in aqueous solutions.

• When ionic compounds dissolve in water, their ions separate in a process called dissociation.

Type of Reactions in Aqueous Solutions

• When two solutions that contain ions as solutes are combined, the ions might react.

• If they react, it is always a double replacement reaction.

• Three products can form: precipitates, water, or gases.


Title: Observe a Precipitate-Forming Reaction, page 301


• Aqueous solutions of sodium hydroxide and copper(II) chloride react to form the precipitate copper(II) hydroxide.2NaOH(aq) + CuCl2(aq) → 2NaCl(aq) + Cu(OH)2(s)

• Ionic equations that show all of the particles in a solution as they actually exist are called complete ionic equations.2Na+(aq) + 2OH–(aq) + Cu2+ (aq)+ 2Cl–(aq) → 2Na+(aq) + 2Cl–(aq) + Cu(OH)2(s)


• Ions that do not participate in a reaction are called spectator ions and are not usually written in ionic equations.

• Formulas that include only the particles that participate in reactions are called net ionic equations.

2OH–(aq) + Cu2+(aq) → Cu(OH)2(s)




• Some reactions produce more water molecules.

• No evidence of a chemical reaction is observable.HBr(aq) + NaOH(aq) → H2O(l) + NaBr(aq)

• Without spectator ions H+(aq) + OH–(aq) → H2O(l).




• Gases that are commonly produced are carbon dioxide, hydrogen cyanide, and hydrogen sulfide.2HI(aq) + Li2S(aq) → H2S(g) + 2LiI(aq)


• Another example is mixing vinegar and baking soda, which produces carbon dioxide gas.

HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)

• H2CO3(aq) decomposes immediately.

H2CO3(aq) → H2O(l) + CO2(g)




• Two reactions can be combined and represented by a single chemical reaction.


Reaction 1 HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)

Reaction 2 H2CO3(aq) → H2O(l) + CO2(g)

Combined equationHCl(aq) + NaHCO3(aq) + H2CO3(aq) → H2CO3(aq) +

NaCl(aq) + H2O(l) + CO2(g)Overall equationHCl(aq) + NaHCO3(aq) → H2O(l) + CO2(g) + NaCl(aq)

Transparency 33: Types of Equations

Math Skills Transparency 12: Simplifying Equations

Homework, Section 3

• SECTION 3 REVIEW, Page 308• Questions #50-56• Answer with complete sentences• Due tomorrow

Key ConceptsSome physical changes are evidence that indicate a chemical

reaction has occurred.

Word equations and skeleton equations provide important information about a chemical reaction.

A chemical equation gives the identities and relative amounts of the reactants and products that are involved in a chemical reaction.

Balancing an equation involves adjusting the coefficients until the number of atoms of each element is equal on both sides of the equation.

Study Guide

SECTION9.1

Reactions and Equations

Classifying chemical reactions makes them easier to understand, remember, and recognize.

Activity series of metals and halogens can be used to predict if single-replacement reactions will occur.

Study Guide

SECTION9.2

Classifying Chemical Reactions

Key Concepts

In aqueous solutions, the solvent is always water. There are many possible solutes.

Many molecular compounds form ions when they dissolve in water. When some ionic compounds dissolve in water, their ions separate.

When two aqueous solutions that contain ions as solutes are combined, the ions might react with one another. The solvent molecules do not usually react.

Reactions that occur in aqueous solutions are double-replacement reactions.

Study Guide

SECTION9.3

Reactions in Aqueous Solutions

Key Concepts

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