1 Modern Chemistry Chapter 8 Chemical Equations and Reactions

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Modern ChemistryModern ChemistryChapter 8Chapter 8

Chemical Equations Chemical Equations and Reactionsand Reactions

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Section 1Section 1

Describing Chemical Reactions

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Indications of a Chemical Indications of a Chemical ReactionReactionProof: one or more substances has

changed identity – chemical change1. Evolution of energy as heat and/or

light2. Production of a gas3. Formation of a precipitate4. Color change

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Ind

icati

on

s of

a R

eact

ion

In

dic

ati

on

s of

a R

eact

ion

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Characteristics of a Chemical Characteristics of a Chemical ReactionReaction1. The equation must represent known

facts.2. The equation must contain the correct

formulas for the reactants and products.

• Diatomic elements: I2 Br2 Cl2 F2 O2 N2 H2

• Molecular elements: S8 P4 (page 263)

3. The law of conservation of mass must be satisfied.

• Coefficients – a whole number that appears in front of a formula in a chemical equation.

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Diatomic ElementsDiatomic Elements

p. 263

Nitrogen gas moleculesNitrogen gas molecules

A Collection of Argon AtomsA Collection of Argon Atoms

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Word and Formula EquationsWord and Formula Equations• Word equations – reactants & products

expressed in words

methane + oxygen carbon dioxide + water

REACTANTS PRODUCTS

YIELDS

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Word and Formula EquationsWord and Formula Equations• Formula equations – reactants &

products expressed with formulas – not balanced

methane + oxygen carbon dioxide + water

STATE OF MATTER SYMBOLS

Solid (s)Liquid (l) Gas (g)Aqueous (aq)

Dissolved in water

CH4 (g) + O2 (g) CO2 (g) + H2O(g)

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Methane CombustionMethane Combustion

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Additional SymbolsAdditional Symbols

p. 226

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Additional SymbolsAdditional Symbols

p. 226

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Balancing Chemical EquationsBalancing Chemical Equations1. If the reaction is described by a

paragraph, write the word equation.

2. Write the formula for each reactant and product to get the formula equation.

3. Balance the equation.4. Insert state of matter symbols and

other additional symbols.

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Balancing Chemical EquationsBalancing Chemical EquationsGOAL OF THE GAME:To get the same number of atom of

each element in the reactant and the product.

To obey the law of conservation of mass.

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Balancing Chemical EquationsBalancing Chemical EquationsRULES OF THE GAME:Only coefficients can be added or

changed.Once formulas are written subscripts

can not be changed.

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Balancing Chemical EquationsBalancing Chemical EquationsTIPS FOR PLAY:Balance the different types of atoms

one at a time.First balance elements that appear

only once on each side.Balance polyatomic ions that appear

on both sides as a single unit.Balance H and O last.

page 271

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Balancing Chemical EquationsBalancing Chemical EquationsTIPS FOR PLAY:Try keeping a tally for each element

on each side below the equation.If it could be balanced by a

coefficient of 1½ - use it- multiply all coefficients in the equation by 2.

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Sample ProblemSample ProblemThe reaction of zinc with aqueous

hydrochloric acid produces a solution of zinc chloride and hydrogen gas. Write a balanced equation for the reaction

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Sample Problem p.272Sample Problem p.272zinc + hydrochloric acid zinc chloride + hydrogen

Zn + HCl ZnCl2 + H2

Zn ClZnCl H HH Cl

2

H Cl

Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2 (g)

Writing EquationsWriting EquationsTwo atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride.

• How many?• Of what?• In what state?

Writing EquationsWriting Equations

Al 2 (s) + 3 CuCl2 (aq)

3Cu (s) + 2 AlCl3(aq)

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Sample Problem Sample Problem Solid aluminum carbide, reacts with

water to produce methane gas, CH4, and solid aluminum hydroxide. Write a balanced chemical equation for this reaction.

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Sample Problem p.273Sample Problem p.273aluminum carbide + water methane + aluminum hydroxide

Al4C3 + H2O CH4 + Al(OH)33

Al =

C =

H =

O =

Al4C3 (s) + 12H2O (l) 3CH4 (g) + 4Al(OH)3 (s)

4

Al =

C =

H =

O =

4

3

2

1

1

1

7

3

4

1

16

12

4

3

24

12

12

4

3

24

12

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Sample Problem Sample Problem Aluminum sulfate and calcium hydroxide

are used in water-purification process. When added to water, they dissolve and react to produce two insoluble products, aluminum hydroxide and calcium sulfate. These products settle out, taking suspended solid impurities with them. Write a balanced chemical equation for the reaction.

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Sample Problem p.273Sample Problem p.273 aluminum sulfate + calcium hydroxide aluminum hydroxide + calcium

sulfateAl2(SO4 )3 + Ca(OH)2 Al(OH)3 +

CaSO4

3

Al =

SO4 =

Ca =

OH =

2

Al =

SO4 =

Ca =

OH =

2

3

1

2

1

1

1

3

2

1

1

6

2

3

3

6

3

2

3

3

6

Al2(SO4)3(aq) + 3Ca(OH)2(aq) 2Al(OH)3(s) + 3CaSO4(s)

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Practice Problems Practice Problems 1. Write word, formula, and balanced

chemical equations for each of the following reactions:

a. Magnesium and hydrochloric acid react to produc magnesium chloride and hydrogen.

b. Aqueous nitric acid reacts with solid magnesium hydroxide to produce aqueous magnesium nitrate and water

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Practice Problems Practice Problems 2. Solid calcium metal reacts with water

to form aqueous calcium hydroxide and hydrogen gas. Write a balanced chemical equation for this reaction.

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Practice ProblemsPractice Problems1. Write balanced chemical equations

for each of the following reactions:a. Solid sodium combines with chlorine

gas to produce solid sodium chloride.b. When solid copper reacts with

aqueous silver nitrate, the products are aqueous copper (II) nitrate and solid silver

c. In a blast furnace, the reaction between solid iron (III) oxide and carbon monoxide gas produces solid iron and carbon dioxide gas.

Describing EquationsDescribing Equations• Describing Coefficients:

– individual atom = “atom”

– covalent substance = “molecule”

– ionic substance = “ formula unit”

3 molecules of carbon dioxide

2 atoms of magnesium

4 formula units of magnesium

oxide

3CO2

2Mg

4MgO

Describing EquationsDescribing Equations• Describing Coefficients:

– Also moles for EVERY type

3 moles of carbon dioxide

2 moles of magnesium

4 moles of magnesium oxide

3CO2

2Mg

4MgO

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Significance of a EquationSignificance of a Equation

Coefficients = molecules (or formula units for ionic or atoms for elements)

4 Fe (s) + 3O2 (g) 2Fe2O3 (s)

4 ATOMS 3 MOLECULES 2 FORMULA UNITS

+

Coefficients = molesConvert moles to grams4mol Fe x 55.85g/1mole = 223.4g

4 MOLES 3 MOLES 2 MOLES

223.4g 96.00 g 319.40g=

Types of Chemical RxN’sTypes of Chemical RxN’s

Section 2

Types of RxN’sTypes of RxN’s

• There are millions of reactions.• Can’t remember them all• Fall into several categories.• We will learn 5 types.• Will be able to predict the products.• For some we will be able to predict

whether they will happen at all.• Will recognize them by the reactants

Types of RxN’sTypes of RxN’s• The classification scheme described in

this section provides an introduction to five basic types of reactions:

• Synthesis (Combination)

• Decomposition • Single-displacement (replacement) • Double-displacement (replacement)• Combustion reactions

Synthesis ReactionsSynthesis Reactions• In a synthesis reaction, also known as a

composition reaction or combination reaction, two or more substances combine to form a new compound.

• This type of reaction is represented by the following general equation.

A + X AX

• A and X can be elements or compounds.

• AX is a compound

Synthesis ReactionsSynthesis Reactions

• 2 elements, or compounds combine to make one compound.

• Ca +O2 CaO

• SO3 + H2O H2SO4

• We can predict the products if they are two elements.

• Mg + N2

Reactions of Elements with Reactions of Elements with OxygenOxygen

• One simple type of synthesis reaction is the combination of an element with oxygen to produce an oxide of the element.

• Almost all metals react with oxygen to form oxides.

• Group 2 elements react in a similar manner, forming oxides with the formula MO, where M represents the metal.

• example: 2Mg(s) + O2(g) 2MgO(s)

SynthesisSynthesis

H2(g) + Cl2(g) 2 HCl(g)

Your Turn IIIYour Turn III

• Ca + Cl2

• Fe + O2 iron (II) oxide

• Al + O2

• Remember that the first step is to write the formula

• Then balance

Decomposition ReactionsDecomposition Reactions

• Decomposition reactions are the opposite of synthesis reactions.

• In a decomposition reaction, a single compound undergoes a reaction that produces two or more simpler substances. s or compounds.

• They are represented by the following general equation.

AX A + X• AX is a compound.

• A and X can be elements or compounds.

Decomposition of Binary Decomposition of Binary CompoundsCompounds

• The decomposition of a substance by an electric current is called electrolysis.

2H2O(l) electricity 2H

2(g) + O

2(g)

2HgO(s) 2Hg(l) + O2(g)

• example:

• Oxides of the less-active metals, which are located in the lower center of the periodic table, decompose into their elements when heated.

• example:

Decomposition ReactionsDecomposition Reactions

Decomposition of Metal Carbonates

CaCO3(s) CaO(s) + CO

2(g)

Ca(OH)2(s) CaO(s) + H

2O(g)

2KClO

3(s)

MnO2 (s) 2KCl(s) + 3O

2(g)

Decomposition of Metal Hydroxides

Decomposition of Metal Chlorates

DecompositionDecomposition

2 H2O(l) 2 H2(g) + O2(g)

Your Turn IVYour Turn IV

• NiCO3

• H2CO3(aq)

Single-Replacement ReactionsSingle-Replacement Reactions

• In a single-replacement reaction, also known as a displacement reaction, one element replaces a similar element in a compound.

• Many single-replacement reactions take place in aqueous solution.

• Single-replacement reactions can be represented by the following general equations.

A + BX AX + B or Y + BX BY + X

• A, B, X, and Y are elements. AX, BX, and BY are compounds.


• One element replaces another• Reactants must be an element and a

compound.• Products will be a different element

and a different compound.• Na + KCl K + NaCl

• F2 + LiCl LiF + Cl2

Single ReplacementSingle Replacement

Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s)


• Metals replace metals (and hydrogen)

• K + AlN • Zn + HCl • Think of water as HOH• Metals replace one of the H,

combine with hydroxide.• Na + HOH

Activity SeriesActivity Series

• We can tell whether a reaction will happen

• Some are more active than other• More active replaces less active • There is a list on page 286• Higher on the list replaces lower.• If the element by itself is higher, it

happens, if lower it doesn’t


• H can be replaced in acids by everything higher

• Only the first 6 (Li - Na) react with water.

• Fe + CuSO4

• Pb + KCl • Al + HCl


• What does it mean that Au And Ag are on the bottom of the list?

• Nonmetals can replace other nonmetals

• Limited to F2 , Cl2 , Br2 , I2

• The order of activity is that on the table.• Higher replaces lower.

• F2 + HCl

• Br2 + KCl

Double-Replacement ReactionsDouble-Replacement Reactions

• In double-replacement reactions, the ions of two compounds exchange places in an aqueous solution to form two new compounds.

• One of the compounds formed is usually a precipitate, an insoluble gas that bubbles out of the solution, or a molecular compound, usually water.

• The other compound is often soluble and remains dissolved in solution.


• A double-displacement reaction is represented by the following general equation.

AX + BY AY + BX

• A, X, B, and Y in the reactants represent ions.

• AY and BX represent ionic or molecular compounds.

Double ReplacementDouble ReplacementPb(NO3)2(aq) + K2CrO4(aq) PbCrO4(s) + 2KNO3(aq)


• The formation of a precipitate occurs when the cations of one reactant combine with the anions of another reactant to form an insoluble or slightly soluble compound.

• example:

2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)

• The precipitate forms as a result of the very strong attractive forces between the Pb2+ cations and the I anions.


• Two things replace each other.• Reactants must be two ionic compounds

or acids.• Usually in aqueous solution

• NaOH + FeCl3

• The positive ions change place.

• NaOH + FeCl3 Fe+3 OH- + Na+1Cl-1

• NaOH + FeCl3 Fe(OH)3 + NaCl


• Will only happen if one of the products– doesn’t dissolve in water and forms a

solid – or is a gas that bubbles out.– or is a covalent compound usually

water.

Your Turn VYour Turn V

• assume all of the reactions take place.

• CaCl2 + NaOH

• CuCl2 + K2S

• KOH + Fe(NO3)3

• (NH4)2SO4 + BaF2

Combustion ReactionsCombustion Reactions

• example: combustion of hydrogen

2H2(g) + O2(g) 2H2O(g)

• example: combustion of propane

C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)

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

Combustion ReactionsCombustion Reactions

• Combustion• A compound composed of only C H

and maybe O is reacted with oxygen• If the combustion is complete, the

products will be CO2 and H2O.

• If the combustion is incomplete, the products will be CO and H2O.

Your Turn VIYour Turn VI

• C4H10 + O2 (complete)

• C4H10 + O2 (incomplete)

• C6H12O6 + O2 (complete)

• C8H8 +O2 (incomplete)

Your Turn VI Part IIYour Turn VI Part IIDistinguish between complete an incomplete

combustion.Write a balanced equation for the complete

combustion of each of these compounds.a) acetic acid, HC2H3O2 c) glycerol, C3H8O3

b) decane, C10H22 d) sucrose, C12H22O11

Write a balanced equation for the incomplete combustion of each of these compounds.a) glycerol, C3H8O3 c) acetic acid, HC2H3O2

b) glucose, C6H12O6 d) acetylene, C2H2

Your Turn VIIYour Turn VII

• Determine the type of reaction and the products and balance.

• H2 + O2

• H2O • Zn + H2SO4 • HgO • KBr +Cl2

• AgNO3 + NaCl

• Mg(OH)2 + H2SO3

Let’s ReviewLet’s Review

• Write out the balanced equation for Copper reacts with chlorine to form copper (II) chloride.

• Write out the balanced equation for Zinc reacts with Hydrochloric acid to form Zinc chloride and hydrogen.

• Write out the balanced equation for Calcium carbonate reacts with Zinc nitride to form Calcium nitride and Zinc carbonate.

Let’s ReviewLet’s Review• Balance the following equations

– C7H16 + O2 ---> CO2 + H2O

– Na2O2 + H2O ---> NaOH + O2

– Al2(SO4)3+Ca(OH)2----> Al(OH)3+CaSO4

– NH3 +HCl ----> NH4Cl

– Ca3(PO4)2 +SiO2 + C ----> CaSiO3 + CO + P


• What type of reaction are the following– Rb + S8 ---> Rb2S

– NH3 + O2 ---> N2 + H2O

– C + SO2 ---> CS2 + CO

– C3H11 + O2 ---> CO2 + H2O

– C5H12 +O2 ---> CO + H2O

– FeCl3 + NH4OH --->Fe(OH)3 + NH4Cl


• Balance them– Rb + S8 ---> Rb2S

– NH3 + O2 ---> N2 + H2O

– C + SO2 ---> CS2 + CO

– C3H11 + O2 ---> CO2 + H2O

– C5H12 +O2 ---> CO + H2O

– FeCl3 + NH4OH --->Fe(OH)3 + NH4Cl


• Predict the products and balance– Sodium phosphate reacts with Lithium

metal.– Butane (C4H10) is completely combusted.– Sodium Chloride reacts with Silver

Hydroxide– Aluminum Bromate reacts with Copper– Potassium reacts with Sulfur– Octane (C8H18) is incompletely combusted


• Predict the products and balance– H2 + O2

– Al2Te3 – Zn + H2SO4 – HgO – KBr +Cl2

– AgNO3 + NaCl

– Mg(OH)2 + H2SO3


• Using the table on Pg 286. Predict if these reactions will occur– Li + BaS – Fe + KCl – Au + HgS – Mn + CuS – Ba + LiS – Na + KCl – HCl + Pb – PbCl2 + H2

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1 Modern Chemistry Chapter 8 Chemical Equations and Reactions