Chapter 6 Chemical Reactions Physical Propertiesfacweb.northseattle.edu/sendsley/stuff/Chem101(SP06)/Lectures/Week... · Chapter 6 Chemical Reactions 6.1 Chemical Changes 6.2 Chemical

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1Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.

Chapter 6 Chemical Reactions

6.1 Chemical Changes

6.2 Chemical Equations

6.3 Balancing a Chemical Equation


The physicalproperties of asubstance are thecharacteristicswe can observeor measurewithout changingthe substance.

Physical Properties


In a physical change,

The identity and composition of thesubstance do not change.

The state can change or the material canbe torn into smaller pieces.

In a chemical change,

New substances form with differentcompositions and properties.

A chemical reaction takes place.

Physical and Chemical Change


Physical and Chemical Change

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Some Examples of Chemical andPhysical Changes


Classify each of the following as a

1) physical change or 2) chemical change

A. ____ Burning a candle.

B. ____ Ice melting on the street.

C. ____ Toasting a marshmallow.

D. ____ Cutting a pizza.

E. ____ Polishing a silver bowl.

Learning Check


Classify each of the following as a

1) physical change or 2) chemical change

A. 2 Burning a candle.

B. 1 Ice melting on the street.

C. 2 Toasting a marshmallow.

D. 1 Cutting a pizza.

E. 2 Polishing a silver bowl.

Solution


Chemical Reaction

In a chemicalreaction, achemical changeproduces one ormore newsubstances.

During a reaction,old bonds arebroken and newbonds are formed.

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In a chemical reaction,atoms in the reactantsare rearranged to formone or more differentsubstances.

In this reaction, Fe andO2 react to form rust(Fe2O3).

4Fe + 3O2 2Fe2O3

Chemical Reaction


A chemical equation Shows the chemical formulas of the reactants to the

left of an arrow and the products on the right. Reactants ProductsMgO + C CO + Mg

Can be read in words. “Magnesium oxide reactswith carbon to form carbon monoxide andmagnesium.”

Writing a Chemical Equation


Symbols Used in Equations

Symbols usedin equationsshow the statesof the reactantsand productsand thereactionconditions.


4 NH3 + 5 O2 4 NO + 6 H2O

Four molecules of NH3 react with fivemolecules of O2 to produce four moleculesof NO and six molecules of H2O.

orFour moles of NH3 react with 5 moles of O2to produce four moles of NO and six molesof H2O.

Quantities in A Chemical Reaction

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In any ordinary chemical reaction, matter is notcreated nor destroyed.

+ + H2 + Cl2 2 HCl

Total atoms = Total atoms 2 H, 2 Cl 2H, 2 Cl

Total Mass = Total Mass2(1.0) + 2(35.5) 2(36.5)73.0 g = 73.0 g

Law of Conservation of Mass


Balancing a Chemical Equation

A chemical equation is balanced when thereare the same numbers of each type of atomon both sides of the equation.

Al + S Al2S3 Not Balanced

2Al + 3S Al2S3 Balanced


To balance an equation, place coefficients in front ofthe appropriate formulas.4 NH3 + 5 O2 4 NO + 6 H2O

Check the balance by counting the atoms of eachelement in the reactants and the products.

4 N (4 x 1N) = 4 N (4 x 1N)12 H (4 x 3H) = 12 H (6 x 2H)10 O (5 x 2O) = 10 O (4O + 6O)

Using Coefficients to Balance


Balance one element at a time.

Use only coefficients to balance.

Fe3O4 + H2 Fe + H2O

Fe: Fe3O4 + H2 3Fe + H2O

O: Fe3O4 + H2 3Fe + 4H2O

H: Fe3O4 + 4H2 3Fe + 4H2O

Steps in Balancing an Equation

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Check the balance of atoms in the following: Fe3O4 + 4 H2 3 Fe + 4 H2O

A. Number of H atoms in products.

1) 2 2) 4 3) 8

B. Number of O atoms in reactants.

1) 2 2) 4 3) 8

C. Number of Fe atoms in reactants.

1) 1 2) 3 3) 4

Learning Check


Fe3O4 + 4 H2 3 Fe + 4 H2O

A. Number of H atoms in products.

3) 8 (4H2O)

B. Number of O atoms in reactants.

2) 4 (Fe3O4)

C. Number of Fe atoms in reactants.

2) 3 (Fe3O4)

Solution


Balancing with Polyatomic Ions

Polyatomic ions can be balanced as a unit whenthey appear on both sides.Pb(NO3)2 + NaCl NaNO3 + PbCl2

Balance NO3- as a unit

Pb(NO3)2 + NaCl 2NaNO3 + PbCl2

2 NO3– = 2 NO3

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Balance Na (or Cl)Pb(NO3)2 + 2NaCl 2NaNO3 + PbCl2

2Na+ = 2Na+

2Cl– = 2Cl–20Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.

Balance each equation. The coefficients in theanswers are read from left to right.

A. __Mg + __N2 __Mg3N2

1) 1, 3, 2 2) 3, 1, 2 3) 3, 1, 1

B.__Al + __Cl2 __AlCl3

1) 3, 3, 2 2) 1, 3, 1 3) 2, 3, 2

Learning Check

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A. 3) 3, 1, 1 3 Mg + 1 N2 1 Mg3N2

B. 3) 2, 3, 2 2 Al + 3 Cl2 2 AlCl3

Solution


A. __Fe2O3 + __C __Fe + __CO2

1) 2, 3, 2,3 2) 2, 3, 4, 3 3) 1, 1, 2, 3

B. __Al + __FeO __Fe + __Al2O3

1) 2, 3, 3, 1 2) 2, 1, 1, 1 3) 3, 3, 3, 1

C. __Al + __H2SO4 __Al2(SO4)3 + __H2

1) 3, 2, 1, 2 2) 2, 3, 1, 3 3) 2, 3, 2, 3

Learning Check


A. 2) 2, 3, 4, 3 2 Fe2O3 + 3 C 4 Fe + 3 CO2

B. 1) 2, 3, 3, 1 2 Al + 3 FeO 3 Fe + 1 Al2O3

C. 2) 2, 3, 1, 3 2 Al + 3 H2SO4 1 Al2(SO4)3 + 3 H2

Solution


6.4 Types of Reactions

Chapter 6 Chemical Reactions

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Chemical reactions are classified intogeneral types:

Combination Decomposition Single Replacement Double Replacement Combustion

Types of Reactions


In a combination reaction, two or moreelements or simple compounds combine toform one product.A + B AB

ExamplesH2 + Cl2 2HCl

2S + 3O2 2SO3

4Fe + 3O2 2Fe2O3

Combination Reactions


In a combination reaction, magnesium andoxygen react to form magnesium oxide.2Mg + O2 2MgO

Combination Reactions

Mg

O2

MgO


In a decomposition reaction, one substance isbroken down (split) into two or more simplersubstances.

AB A + B

2HgO 2Hg + O2

2KClO3 2KCl + 3 O2

Decomposition Reactions

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Classify the following reactions as

1) combination or 2) decomposition:

___A. H2 + Br2 2HBr

___B. Al2(CO3)3 Al2O3 + 3CO2

___C. 4 Al + 3C Al4C3

Learning Check


Classify the following reactions as

1) combination or 2) decomposition:

1 A. H2 + Br2 2HBr

2 B. Al2(CO3)3 Al2O3 + 3CO2

1 C. 4 Al + 3C Al4C3

Solution


In a single replacement, one element takes theplace of an element in a reacting compound.A + BC AC + BZn(s) + HCl(aq) ZnCl2(aq) + H2(g)

Single Replacement

Zn HCl

H2

ZnCl2


In a double replacement, the positive ions inthe reacting compounds switch places.

AB + CD AD + CB

AgNO3 + NaCl AgCl + NaNO3

ZnS + 2HCl ZnCl2 + H2S

Double Replacement

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Example of a Double Replacement

When solutions of sodium sulfate and bariumchloride are mixed, solid BaSO4 is produced.

BaCl2 + Na2SO4 BaSO4 + 2NaCl

BaSO4


Classify each of the following reactions as a

1) single replacement or 2) double replacement

__A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2

__B. Na2SO4 + 2AgNO3 Ag2SO4 + 2NaNO3

__C. 3C + Fe2O3 2Fe + 3CO

Learning Check


Classify each of the following reactions as a

1) single replacement or 2) double replacement

1 A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2

2 B. Na2SO4 + 2AgNO3 Ag2SO4 + 2NaNO3

1 C. 3C + Fe2O3 2Fe + 3CO

Solution


In a combustion reaction, a reactant oftencontaining carbon reacts with oxygen O2.

C + O2 CO2

CH4 + 2O2 CO2 + 2H2O

C3H8 + 5O2 3CO2 + 4H2O

Many combustion reactions utilize fuels thatare burned in oxygen to produce CO2, H2O,and energy.

Combustion

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Balance the combustion equation:

___C5H12 + ___O2 ___CO2 + ___H2O

Learning Check


Balance the combustion equation:

1 C5H12 + 8 O2 5 CO2 + 6 H2O

Solution


Summary of Reaction Types


Learning Check

Identify each reaction as 1) combination 2) decomposition 3) combustion4) single replacement 5) double replacementA. 3Ba + N2 Ba3N2

B. 2Ag + H2S Ag2S + H2

C. SiO2 + 4HF SiF4 + 2H2O

D. PbCl2 + K2SO4 2KCl + PbSO4

E. K2CO3 K2O + CO2

F. C2H4 + 3O2 2CO2 + 2H2O

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Solution

Identify each reaction as 1) combination 2) decomposition 3) combustion4) single replacement 5) double replacement 1 A. 3Ba + N2 Ba3N2

4 B. 2Ag + H2S Ag2S + H2

5 C. SiO2 + 4HF SiF4 + 2H2O 5 D. PbCl2 + K2SO4 2KCl + PbSO4

2 E. K2CO3 K2O + CO2

3 F. C2H4 + 3O2 2CO2 + 2H2O

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Chapter 6 Chemical Reactions Physical Propertiesfacweb.northseattle.edu/sendsley/stuff/Chem101(SP06)/Lectures/Week... · Chapter 6 Chemical Reactions 6.1 Chemical Changes 6.2 Chemical