Chemical ReactionsChemical ReactionsChapter 11Chapter 11

General Chemistry

ObjectivesObjectives• Balance chemical equations by applying Balance chemical equations by applying

the law of conservation of mass. the law of conservation of mass. • Recognize synthesis, decomposition, Recognize synthesis, decomposition,

single displacement, double single displacement, double displacement, and neutralization displacement, and neutralization reactions.reactions.

• Write chemical equations from words.Write chemical equations from words.• Predict the products of chemical Predict the products of chemical

reactions.reactions.• Write net ionic equations for reactions.Write net ionic equations for reactions.

Chemical Reactions Chemical Reactions BasicsBasics

Chemical ReactionsChemical Reactions

A A chemical reactions chemical reactions are chemical are chemical changes.changes.

Recall: chemical changes are when Recall: chemical changes are when one or more substances are changed one or more substances are changed into different substancesinto different substances• Examples: wood burning, metal rustingExamples: wood burning, metal rusting

Indications of a Chemical ReactionIndications of a Chemical Reaction Certain easily observed changes indicate Certain easily observed changes indicate

that a chemical reaction has occurred:that a chemical reaction has occurred: evolution of energy by heat and/or lightevolution of energy by heat and/or lightcolor changecolor changeproduction of gasproduction of gasproduction of precipitateproduction of precipitate

A solid that is produced as a result of a chemical A solid that is produced as a result of a chemical reaction in solution and that separates from the reaction in solution and that separates from the solution is known as asolution is known as a precipitateprecipitate

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Law of Conservation of MatterLaw of Conservation of Matter Chemical reactions obey the Law of Chemical reactions obey the Law of

Conservation of MatterConservation of Matter

in all chemical and physical changes, in all chemical and physical changes, matter is neither created or destroyedmatter is neither created or destroyed

The total mass in a chemical reaction The total mass in a chemical reaction remains constantremains constant

Chemical EquationsChemical Equations A A chemical equation chemical equation represents, with symbols and represents, with symbols and

formulas, the identities and the amounts of the formulas, the identities and the amounts of the reactants and products in a chemical reaction.reactants and products in a chemical reaction.

Has two parts: Has two parts: • Reactants:Reactants: the substances you start with the substances you start with• Products:Products: the substances you end up with the substances you end up with

The reactants turn into the productsThe reactants turn into the products

4 Fe + 3 O4 Fe + 3 O22 2 Fe 2 Fe22OO33

Reactants Reactants products products

Ways to Express a Chemical Ways to Express a Chemical ReactionReaction

The way atoms are joined is changed in a The way atoms are joined is changed in a chemical reaction.chemical reaction.Can be described several ways:Can be described several ways:

1. In a 1. In a sentence sentence Copper reacts with chlorine to form copper (II) Copper reacts with chlorine to form copper (II)

chloride.chloride.

2. In a 2. In a word equationword equationCopper + chlorine Copper + chlorine copper (II) chloride copper (II) chloride

3. In 3. In formula equationformula equation::Cu + ClCu + Cl22 CuCl CuCl22

Symbols Used in Chemical Symbols Used in Chemical EquationsEquations

Additional Symbols Used in Additional Symbols Used in EquationsEquations

shows that shows that heat heat is supplied to the is supplied to the reactionreaction

is used to indicate a is used to indicate a catalystcatalyst is supplied, in this case, is supplied, in this case, platinum.platinum.

heat ,

Pt

What is a catalyst?What is a catalyst?

A A catalystcatalyst is a substance that is a substance that speeds up a reaction, without speeds up a reaction, without being changed or used up by the being changed or used up by the reaction.reaction.Enzymes are biological or protein Enzymes are biological or protein

catalysts.catalysts.

Study Buddy ReviewStudy Buddy Review

What are four things that indicate a What are four things that indicate a chemical reaction has taken place?chemical reaction has taken place?

What is the Law of Conservation of What is the Law of Conservation of mass?mass?

What does the symbol (l) mean?What does the symbol (l) mean? What does (aq) mean?What does (aq) mean?

Balancing Chemical Balancing Chemical EquationsEquations

Skeleton and Balanced Skeleton and Balanced EquationsEquations

Skeleton equations: Skeleton equations: do not do not indicate how many of each indicate how many of each element/compound element/compound

Balanced equations:Balanced equations: the number the number of atoms of each element is the of atoms of each element is the same on both sides of the same on both sides of the reaction.reaction.

Numbers in Balanced EquationsNumbers in Balanced Equations

Use coefficients to balance equationUse coefficients to balance equation

Coefficients:Coefficients: large whole numbers placed large whole numbers placed in front of formula which represents in front of formula which represents number of units of that compoundnumber of units of that compound

Subscript:Subscript: small whole number placed in small whole number placed in chemical formula to represent number of chemical formula to represent number of atoms of an element in a compoundatoms of an element in a compound

4 Fe + 3 O4 Fe + 3 O22 2 Fe 2 Fe22OO33

Coefficient subscript

Balanced EquationBalanced Equation

A A balanced equation balanced equation has the has the same number of atoms of each same number of atoms of each element on both sides of the element on both sides of the equationequation

Atoms can’t be created or Atoms can’t be created or destroyeddestroyed

All the atoms at the beginning All the atoms at the beginning must appear in the endmust appear in the end

C + OC + O22 CO CO We need one more oxygen in the We need one more oxygen in the

products.products. Can’t change the formula, because it Can’t change the formula, because it

describes what it is (carbon monoxide in describes what it is (carbon monoxide in this example)this example)

C + O COO

Must be used to make another COMust be used to make another CO But where did the other C come from?But where did the other C come from?

C +O

C

OO

OC

Must have started with two CMust have started with two C 2 C + O2 C + O22 2 CO 2 CO

C

+O

C

OO

OC

C

Rules for balancing:Rules for balancing:

Assemble, write the Assemble, write the correct formulascorrect formulas for for all the reactants and productsall the reactants and products

Count the number of atoms of each type Count the number of atoms of each type of element appearing on both sidesof element appearing on both sides

Balance the atoms of an element one at a Balance the atoms of an element one at a time by adding coefficients (the numbers time by adding coefficients (the numbers in front) - save H and O until LAST!in front) - save H and O until LAST!

Check to make sure it is balanced.Check to make sure it is balanced.

Never change a subscript to balance an Never change a subscript to balance an equation.equation.• If you change the formula you are If you change the formula you are

describing a different reaction.describing a different reaction.

• HH22O is a different compound than HO is a different compound than H22OO22

Never put a coefficient in the middle of Never put a coefficient in the middle of a formulaa formula• 2 NaCl is okay, Na2Cl is not.2 NaCl is okay, Na2Cl is not.

Balancing Equations ExamplesBalancing Equations Examples

HH22 (g) (g) + O+ O22 (g) (g) H H22O (l)O (l)

Zn + HCl Zn + HCl H H22 + ZnCl + ZnCl22

Pb (NOPb (NO33))22 + K + K22S S PbS + KNO PbS + KNO33

Balancing Equations Balancing Equations AnswersAnswers

22 H H22 (g) (g) + O+ O22 (g) (g) 22 H H22O (l)O (l)

Zn + Zn + 22 HCl HCl H H22 + ZnCl + ZnCl22

Pb (NOPb (NO33))22 + K + K22S S 22PbS + PbS + 22KNOKNO33

Word Equation ExamplesWord Equation Examples

Write a balanced chemical equation Write a balanced chemical equation for the following:for the following:

Aqueous solutions of sulfuric acid Aqueous solutions of sulfuric acid and sodium hydroxide react to form and sodium hydroxide react to form aqueous sodium sulfate and water.aqueous sodium sulfate and water.

Five General Types of Five General Types of Chemical ReactionsChemical Reactions

Five General Types of Five General Types of Chemical ReactionsChemical Reactions

1.1. Synthesis (Composition)Synthesis (Composition)

2.2. DecompositionDecomposition

3.3. Single-ReplacementSingle-Replacement

4.4. Double-ReplacementDouble-Replacement

5.5. CombustionCombustion

By knowing the type of reaction that is By knowing the type of reaction that is occurring, you can predict the products occurring, you can predict the products that will be formed.that will be formed.

General Types of Chemical General Types of Chemical ReactionsReactions

Combination: Combination: A + B A + B AB AB Decomposition: Decomposition: AB AB A + B A + B Single Replacement :Single Replacement :

AX +B AX +B A + BX A + BX Double Replacement: Double Replacement:

AX + BY AX + BY AY + BX AY + BX Combustion:Combustion:

CCxxHHyy + O+ O22 CO CO22 + H + H22OO

Synthesis (Combination)

General form: A + B AB (two reactants make a single product)

A, B = elements or compoundsAB = compound consisting of A and B

This is the only type of chemical reaction in which there is a single product formed. This single product is

always more complex than the reactants.

Examples of Synthesis Reactions

a. calcium + oxygen yields calcium oxide 2Ca + O2 2CaO

b. carbon dioxide + water yields carbonic acidCO2 + H2O H2CO3

Notice: All equations show two (or more) reactants, but only one product.

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Decomposition ReactionsDecomposition Reactions

(Decomposing = breaking down into (Decomposing = breaking down into smaller parts; microorganisms)smaller parts; microorganisms)

A reaction in which a single compound is A reaction in which a single compound is broken into 2 or more smaller compounds broken into 2 or more smaller compounds or elements. The opposite of direct or elements. The opposite of direct combination/synthesis.combination/synthesis.

You can identify this reaction because there You can identify this reaction because there is only one reactant.is only one reactant.

General form: General form: AB AB A + B A + B AB = compoundAB = compound

A, B = elements or simpler compoundsA, B = elements or simpler compounds

Examples of Decomposition Examples of Decomposition ReactionsReactions

Water yields hydrogen and oxygenWater yields hydrogen and oxygen

2H2H22O O 2H 2H2 2 + O + O22

marble (rock) yields (with heating) marble (rock) yields (with heating) calcium oxide and carbon dioxidecalcium oxide and carbon dioxide

CaCOCaCO3 3 CaO + CO CaO + CO22

Notice: single compound decomposes Notice: single compound decomposes into two (or more) products.into two (or more) products. http://www.ric.edu/ptiskus/reactions/Index.htm

Single-Replacement ReactionsSingle-Replacement Reactions

One element and one compound One element and one compound recombine (switch partners)recombine (switch partners)

General Form: A + BX General Form: A + BX AX + B AX + B

AX, BX = ionic compoundsAX, BX = ionic compounds

A, B = elementsA, B = elements

X = ion that switches partnersX = ion that switches partners

Examples of Single-Replacement Examples of Single-Replacement ReactionsReactions

Magnesium metal and copper (II) Magnesium metal and copper (II) sulfatesulfate

Mg + CuSOMg + CuSO4 4 MgSO MgSO44 + Cu + Cu

Iron metal and copper (II) sulfate)Iron metal and copper (II) sulfate)

Fe + CuSOFe + CuSO44 FeSO FeSO44 + Cu + Cu

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Double-Replacement ReactionsDouble-Replacement Reactions

Positive ions in two compounds are Positive ions in two compounds are exchanged.exchanged.

Look for: 2 compounds as reactants and Look for: 2 compounds as reactants and 2 compounds as products.2 compounds as products.

Reactants are usually ionic compounds.Reactants are usually ionic compounds. Specific example: neutralization Specific example: neutralization

reactions between acid and basereactions between acid and base

General form: AX + BY General form: AX + BY AY + BX AY + BX

(Notice: X and Y “change partners”)(Notice: X and Y “change partners”)

Examples of Double Replacement Examples of Double Replacement ReactionsReactions

Calcium carbonate and hydrochloric Calcium carbonate and hydrochloric acid yield calcium chloride and acid yield calcium chloride and carbonic acid.carbonic acid.

CaCOCaCO33 + 2HCl + 2HCl CaCl CaCl22 + H + H22COCO33

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Rules of Double-Displacement Rules of Double-Displacement ReactionsReactions

Reactants must be dissolved in Reactants must be dissolved in water (releasing the ions).water (releasing the ions).

Will occur ifWill occur if::1.1. One of the products is a molecule One of the products is a molecule

(covalent), (covalent),

2.2. A precipitate (solid comes out of A precipitate (solid comes out of solution), orsolution), or

3.3. An insoluble gas.An insoluble gas.

Combustion ReactionsCombustion Reactions

Reactants: Reactants: a fuel (usually a hydrocarbon) a fuel (usually a hydrocarbon) and oxygen.and oxygen.

Products: Products: water, carbon dioxide, and lots water, carbon dioxide, and lots of energy! (heat, light)of energy! (heat, light)

Examples: Examples: CHCH44 (methane) + 2O (methane) + 2O2 2 2H 2H22O + COO + CO22

CC22HH55OH (gasohol) + 3OOH (gasohol) + 3O22 3H 3H22O + 2COO + 2CO22

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Study Buddy ReviewStudy Buddy Review

Describe each of the following to your Describe each of the following to your study buddy:study buddy:

• Synthesis (combination)Synthesis (combination)• DecompositionDecomposition• Single-ReplacementSingle-Replacement• Double-ReplacementDouble-Replacement• CombustionCombustion

Activity SeriesActivity Series

Activity Series and Single Activity Series and Single Replacement ReactionsReplacement Reactions

AlAl ++ CuClCuCl22 ??? ???

Cu +Cu + AlClAlCl33 ??? ???

Only one of the following reactions Only one of the following reactions will occurwill occur

How do you know which one? How do you know which one?

Activity Series of MetalsActivity Series of Metals

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Activity Series RulesActivity Series Rules

Elements at top of series are most Elements at top of series are most activeactive

Elements at bottom of series are least Elements at bottom of series are least active (coinage metals)active (coinage metals)

Elements at the top of the series will Elements at the top of the series will replace elements replace elements below it below it in a chemical in a chemical reaction.reaction.

Example: Al + CuClExample: Al + CuCl22 will occur will occur

Cu + AlClCu + AlCl33 will NOT occur will NOT occur

Activity Series ExamplesActivity Series Examples

Using the activity series, predict Using the activity series, predict whether each of the possible whether each of the possible reactions will occur:reactions will occur:• Cr + HCr + H22O O

• Pt + OPt + O22

• Cd + 2HBr Cd + 2HBr

Activity Series ExamplesActivity Series Examples

Using the activity series, predict Using the activity series, predict whether each of the possible whether each of the possible reactions will occur:reactions will occur:• Cr + HCr + H22O O NRNR

• Pt + OPt + O22 NRNR

• Cd + 2HBr Cd + 2HBr CdBrCdBr22 + H + H22

ReferencesReferences

Dr. Stephen L. Cotton Charles Dr. Stephen L. Cotton Charles Page High SchoolPage High School

Mrs. LijekMrs. Lijek