Chapter 8Chapter 8

Chemical Equations and Chemical Equations and ReactionsReactions

8.1 Describing Chemical 8.1 Describing Chemical EquationsEquations

Indicators of Chemical Indicators of Chemical ReactionsReactions

• Evolution of Heat & Light- ExothermicEvolution of Heat & Light- Exothermic

• Production of a Gas: COProduction of a Gas: CO22, H, H22, H, H22SS

• Formation of a PrecipitateFormation of a PrecipitateBaClBaCl22 (aq)(aq) + Na + Na22SOSO44 (aq)(aq) → 2NaCl → 2NaCl (aq)(aq) + BaSO + BaSO44 (s)(s)

Chemical EquationsChemical Equations

• A formula equation uses symbols & A formula equation uses symbols & formulas to represent the identities & formulas to represent the identities & relative amounts of reactants & products. relative amounts of reactants & products.

• There are also word equations which use There are also word equations which use chemical names instead of formulas. chemical names instead of formulas.

• See p. 246 TableSee p. 246 Table

Reactants (s) Reactants (s) → Products (g)→ Products (g)

State of MatterState of Matter

Original Original SubstancesSubstances

Resulting Resulting SubstancesSubstances

Chemical EquationsChemical Equations

• Equations Equations mustmust::– Represent known facts.Represent known facts.– Contain Contain correctcorrect formulas for all formulas for all

compounds.compounds.– Satisfy the law of conservation of mass.**Satisfy the law of conservation of mass.**

** This is called balancing the equation.** This is called balancing the equation.

Balancing EquationsBalancing Equations

• RULE: The number and type of atoms on the RULE: The number and type of atoms on the left side of the equation must equal the left side of the equation must equal the number and type of atoms on the rightnumber and type of atoms on the right

• Example:Example:

HH22O O →→ H H22 + O + O22 *not OK*not OK

• missing 1 oxygen on the left side of the missing 1 oxygen on the left side of the equationequation

Balancing EquationsBalancing Equations

Sodium + Chlorine Sodium + Chlorine → Sodium Chloride→ Sodium Chloride

Na Na (s)(s) + Cl + Cl22 (g)(g) → NaCl → NaCl (s)(s)

Na Na ClCl Na Na ClCl

11 22 11 11

Balancing EquationsBalancing Equations

Sodium + Chlorine Sodium + Chlorine → Sodium Chloride→ Sodium Chloride

22Na Na (s)(s) + Cl + Cl22 (g)(g) → → 22NaCl NaCl (s)(s)

Na Na ClCl Na Na ClCl

22 22 22 22Must be Must be

the the smallest smallest Ratio!Ratio!

Add Add coefficients coefficients

to the front of to the front of a formula!a formula! 2 Na : 1 Cl2 Na : 1 Cl22 : 2 NaCl : 2 NaCl

Coefficients vs. SubscriptsCoefficients vs. Subscripts

CHCH44 + 2O + 2O22 → → COCO22 + 2H + 2H22OO

• NEVER change subscript, only the NEVER change subscript, only the coefficient when balancing!!!coefficient when balancing!!!

SubscriptSubscript CoefficientCoefficient

Steps for Balancing EquationsSteps for Balancing Equations

• Identify the names of reactants and products, Identify the names of reactants and products, and write a word equation.and write a word equation.

• Write a formula equation by substituting Write a formula equation by substituting correct formulascorrect formulas for the names of the for the names of the reactants and the products. reactants and the products.

• Balance the formula equation according to Balance the formula equation according to the the law of conservation of masslaw of conservation of mass. .

• Count atoms on both sides to be sure that Count atoms on both sides to be sure that the equation is balanced!the equation is balanced!

Balancing EquationsBalancing Equations

• The coefficients indicate relative amounts The coefficients indicate relative amounts of substances, a ratio. of substances, a ratio.

HH22 (g)(g) + Cl + Cl22 (g)(g) → → 22HCl HCl (g)(g)

1 mole 1 mole HH2 2 : 1 mole Cl: 1 mole Cl22 : 2 mole : 2 mole HClHCl

Now, convert the moles to mass values to Now, convert the moles to mass values to indicate the relative masses!indicate the relative masses!

PracticePractice

• Write the Word Equation:Write the Word Equation:

FeS FeS (aq)(aq) + H + H22SOSO44 (aq)(aq) → FeSO → FeSO44 (aq)(aq) + H + H22S S (g)(g)

Iron (II) + Sulfuric → Iron (II) + Hydrosulfuric Iron (II) + Sulfuric → Iron (II) + Hydrosulfuric

Sulfide Sulfide Acid Acid Sulfate Sulfate AcidAcid

PracticePractice

• Write the formula equation.Write the formula equation.Sodium + Carbon + Water Sodium + Carbon + Water (g)(g) → Sodium Hydrogen→ Sodium Hydrogen

Oxide Oxide (s)(s) Dioxide Dioxide (g)(g) Carbonate Carbonate (s)(s)

NaNa22O O (s)(s) + CO + CO22 (g)(g) + H + H22O O (g)(g) → NaHCO→ NaHCO33 (s)(s)

• Now balance the equation!Now balance the equation!

NaNa22O O (s)(s) + + 22COCO22 (g)(g) + H + H22O O (g)(g) → → 22NaHCONaHCO33 (s)(s)

• Now…. Translate into a sentence!Now…. Translate into a sentence!

Chapter 8Chapter 8

Chemical Equations and Chemical Equations and ReactionsReactions

8.2 Types of Chemical 8.2 Types of Chemical ReactionsReactions

Types of ReactionsTypes of Reactions

• Most chemical reactions can be Most chemical reactions can be classified into 5 major categories:classified into 5 major categories:

SynthesisSynthesis

DecompositionDecomposition

Single Replacement (Displacement)Single Replacement (Displacement)

Double Replacement (Displacement)Double Replacement (Displacement)

CombustionCombustion

Synthesis (Composition) Synthesis (Composition) ReactionsReactions

A + X A + X AX AX

Reaction of elements with oxygen to form oxidesReaction of elements with oxygen to form oxides Reactions of elements with sulfur to form sulfidesReactions of elements with sulfur to form sulfides Nonmetals react with oxygen to form oxidesNonmetals react with oxygen to form oxides Reactions of halogens to form saltsReactions of halogens to form salts Active metal oxides react with water to form metallic Active metal oxides react with water to form metallic hydroxideshydroxides Nonmetal oxides react with water to form oxyacids Nonmetal oxides react with water to form oxyacids

(acid rain)(acid rain)

Two or more Two or more substances substances

combine to form a combine to form a new compound.new compound.

Synthesis Synthesis ReactionsReactions

• Reaction of elements with oxygen to Reaction of elements with oxygen to form oxides:form oxides:

4Al 4Al (s)(s) + 3O + 3O22 (g)(g) → 2Al → 2Al22OO33 (s)(s)

• Reactions of elements with sulfur to Reactions of elements with sulfur to form sulfides:form sulfides:

8Ba 8Ba (s)(s) + S + S88 (s)(s) → 8BaS → 8BaS (s)(s)

??????

??????

2 or more 2 or more substances substances

combine to form combine to form a more complex a more complex

substancesubstance..

Synthesis ReactionsSynthesis Reactions

• Nonmetals react with oxygen to form Nonmetals react with oxygen to form oxidesoxides::

C C (s)(s) + O + O22 (g)(g) → CO → CO22 (g)(g)

• Reactions of halogens to form saltsReactions of halogens to form salts::

2Na 2Na (s)(s) + Cl + Cl22 (g)(g) → 2NaCl → 2NaCl (s)(s)

??????

??????

Multiple ReactantsMultiple Reactants One ProductOne Product

Synthesis ReactionsSynthesis Reactions

• Active metal oxides react with water to Active metal oxides react with water to form metallic hydroxides:form metallic hydroxides:

MgO MgO (s)(s) + H + H22O O (l)(l) → Mg(OH) → Mg(OH)22 (s)(s)

• Nonmetal oxides react with water to Nonmetal oxides react with water to form oxyacids (acid rain):form oxyacids (acid rain):

SOSO22 (g)(g) + H + H22O O (l)(l) → H → H22SOSO33 (aq)(aq)

??????

??????

Decomposition ReactionsDecomposition Reactions

Decomposition of:Decomposition of:

1.1. Binary compounds Binary compounds (electric current)(electric current)

2.2. Metal carbonates Metal carbonates 3.3. Metal hydroxidesMetal hydroxides4.4. Metal chlorates Metal chlorates 5.5. OxyacidsOxyacids

AX AX A + X A + XA single compound A single compound

undergoes a reaction undergoes a reaction that that

produces two or more produces two or more simpler substancessimpler substances

DecompositionDecompositionAX AX → A + X→ A + X

1.1. 2H2H22O O (l)(l) 2H 2H22 (g)(g) + O + O22 (g)(g)

2.2. CaCOCaCO33 (s)(s) CaO CaO (s)(s) + CO + CO22 (g)(g)

3.3. Ca(OH)Ca(OH)22 (s)(s) CaO CaO (s)(s) + H + H22O O (g)(g)

4.4. 2KClO2KClO33 (s)(s) 2KCl 2KCl (s)(s) + 3O + 3O22 (g)(g)

5.5. HH22COCO33 (aq)(aq) CO CO22 (g)(g) + H + H22O O (l)(l)

One complex One complex substance breaks down substance breaks down

into simpler into simpler substancessubstances..

??????

??????

Single Replacement Single Replacement (Displacement) Reactions(Displacement) Reactions

Replacement ofReplacement of::

1.1. Metals by a more active metalMetals by a more active metal

2.2. Hydrogen in water by an active metalHydrogen in water by an active metal

3.3. Hydrogen in an acid by a metalHydrogen in an acid by a metal

4. Halogens by more active halogens4. Halogens by more active halogens

A + BX A + BX AX + B AX + B

BX + Y BX + Y BY + X BY + X

Single ReplacementSingle ReplacementA + BX A + BX → B + AX→ B + AXBX + Y → BY + XBX + Y → BY + X

1.1. Zn Zn (s)(s) + CuSO + CuSO44 (aq)(aq) → ZnSO → ZnSO44 (aq)(aq) + Cu + Cu (s)(s)

2.2. Ca Ca (s)(s) + 2H + 2H22O O (l)(l) → Ca(OH) → Ca(OH)22 (aq)(aq) + H + H22 (g)(g)

3.3. Zn Zn (s)(s) + H + H22SOSO44 (aq)(aq) → ZnSO → ZnSO44 (aq)(aq) + H + H22 (g)(g)

4.4. ClCl22 (g)(g) + 2KBr + 2KBr (aq)(aq) → 2KCl → 2KCl (aq)(aq) + Br + Br22 (g)(g)

One element takes the One element takes the place of another in a place of another in a

compound.compound.

??????

??????

Double Replacement Double Replacement (Displacement) Reactions(Displacement) Reactions

The ions of two compoundsThe ions of two compounds exchange placesexchange places in anin anaqueous solution to form two new compounds.aqueous solution to form two new compounds.

AX + BY AX + BY AY + BX AY + BX

One of the compounds formed is usually a One of the compounds formed is usually a precipitateprecipitate, an , an insoluble gasinsoluble gas that bubbles out of that bubbles out ofsolution, or a solution, or a molecular compoundmolecular compound, usually water., usually water.

Double ReplacementDouble Replacement AX + BY → AY + BXAX + BY → AY + BX

BaClBaCl22 (aq)(aq) + Na + Na22SOSO44 (aq)(aq) → 2NaCl → 2NaCl (aq)(aq) + + BaSOBaSO44 (s)(s)

FeS FeS (aq)(aq) + H + H22SOSO44 (aq)(aq) → FeSO → FeSO44 (aq)(aq) + + HH22S S (g)(g)

NaOH NaOH (aq)(aq) + HCl + HCl (aq)(aq) → NaCl → NaCl (aq)(aq) + + HH22O O (l)(l)

Ions of 2 Ions of 2 compounds compounds exchange exchange places to places to

form 2 new form 2 new compoundscompounds

ProduceProduce

s a solid, s a solid,

gas or gas or

water!water!

PrecipitatePrecipitate

GasGas

WaterWater

??????

Combustion Combustion ReactionsReactions

A substance combines with A substance combines with oxygen, releasing a large oxygen, releasing a large

amount of energy in the form of amount of energy in the form of light and heat.light and heat.

Reactive elements combine with oxygenReactive elements combine with oxygen

PP4 (s)4 (s) + 5O + 5O2 (g)2 (g) P P44OO10 (s)10 (s)

(This is also a synthesis reaction)(This is also a synthesis reaction)

The burning of natural gas, wood, gasolineThe burning of natural gas, wood, gasoline

CC33HH8 (g)8 (g) + 5O + 5O2 (g)2 (g) 3CO 3CO2 (g)2 (g) + 4H + 4H22O O (g)(g)

(The products are (The products are ALWAYSALWAYS carbon dioxide & water) carbon dioxide & water)

Chapter 8Chapter 8

Chemical Equations and Chemical Equations and ReactionsReactions

8.3 Activity Series of the 8.3 Activity Series of the ElementsElements

The Activity SeriesThe Activity Series LithiumLithium PotassiumPotassium CalciumCalcium SodiumSodium MagnesiumMagnesium AluminumAluminum ZincZinc ChromiumChromium IronIron NickelNickel LeadLead HydrogenHydrogen BismuthBismuth CopperCopper MercuryMercury SilverSilver PlatinumPlatinum GoldGold

Metals can replace other metals,Metals can replace other metals,provided that they are above theprovided that they are above themetal that they are trying to metal that they are trying to replace.replace.

Metals above hydrogen can Metals above hydrogen can replace hydrogen in acids.replace hydrogen in acids.

Metals from sodium upward canMetals from sodium upward canreplace hydrogen in water.replace hydrogen in water.

De

creasin

g A

ctivityD

ecrea

sing

Activity

Activity Series GuidelinesActivity Series Guidelines• All metals above hydrogen displace hydrogen from All metals above hydrogen displace hydrogen from

hydrochloric acid or dilute sulfuric acid. hydrochloric acid or dilute sulfuric acid. HCl or HHCl or H22SOSO4 4

• Metals above magnesium vigorously displace hydrogen Metals above magnesium vigorously displace hydrogen from water. Magnesium displaces hydrogen from steam. from water. Magnesium displaces hydrogen from steam. Mg(OH)Mg(OH)2 2

• Metals above silver combine directly with oxygen; those Metals above silver combine directly with oxygen; those near the top do so rapidly. near the top do so rapidly.

• Metals below mercury form oxides only indirectly.Metals below mercury form oxides only indirectly.

• Oxides of metals below mercury decompose with mild Oxides of metals below mercury decompose with mild heating. heating.

Activity Series GuidelinesActivity Series Guidelines• Oxides of metals below chromium easily undergo Oxides of metals below chromium easily undergo

reduction to metals by heating with hydrogen.reduction to metals by heating with hydrogen.

• Oxides of metals above iron resist reduction by Oxides of metals above iron resist reduction by heating with hydrogen.heating with hydrogen.

• Elements near the top of the series are never found Elements near the top of the series are never found free in nature. free in nature. (highly reactive)(highly reactive)

• Elements near the bottom of the series are often Elements near the bottom of the series are often found free in nature.found free in nature. (mildly reactive)(mildly reactive)

The Activity Series of the The Activity Series of the HalogensHalogens

FluorineFluorine ChlorineChlorine BromineBromine IodineIodine

Halogens can replace other Halogens can replace other halogens in compounds, providedhalogens in compounds, providedthat they are above the halogenthat they are above the halogenthat they are trying to replace.that they are trying to replace.

2NaCl (s) + F2NaCl (s) + F2 2 (g) (g) 2NaF (s) + Cl2NaF (s) + Cl2 2 (g)(g)

MgClMgCl2 2 (s) + Br(s) + Br2 2 (g) (g) ??????No ReactionNo Reaction

??????

De

creasin

g A

ctivityD

ecrea

sing

Activity

Practice:Practice:

1.1. Cu Cu (s)(s) + AgNO + AgNO33 (aq)(aq) → ? → ?

2.2. Zn Zn (s)(s) + CuSO + CuSO44 (aq)(aq) → ? → ?

3.3. NaNa22O O (s)(s) + CO + CO22 (g)(g) + H + H22O O (g)(g) → ? → ?

4.4. HH22SOSO44 (aq)(aq) + BaCl + BaCl22 (aq)(aq) → ? → ?

5.5. AlAl22OO33 (s)(s) + H + H22SOSO44 (aq)(aq) → ? → ?

Complete and balance the Complete and balance the reactions, if they will occur… reactions, if they will occur…

SRSR

SRSR

SS

DRDR

DRDR

Practice:Practice:

1.1. Cu Cu (s)(s) + 2AgNO + 2AgNO33 (aq)(aq) → ? → ?

2.2. Zn Zn (s)(s) + CuSO + CuSO44 (aq)(aq) → ? → ?

3.3. NaNa22O O (s)(s) + 2CO + 2CO22 (g)(g) + H + H22O O (g)(g) → ? → ?

4.4. HH22SOSO44 (aq)(aq) + BaCl + BaCl22 (aq)(aq) → ? → ?

5.5. AlAl22OO33 (s)(s) + 3H + 3H22SOSO44 (aq)(aq) → ? → ?

Complete and balance the Complete and balance the reactions, if they will occur… reactions, if they will occur…

SRSR

SRSR

SS

DRDR

DRDR

2NaHCO2NaHCO33 (s)(s)

2HCl 2HCl (aq)(aq) + BaSO + BaSO44 (s)(s)

AlAl22(SO(SO44))33 (aq)(aq) + 3H + 3H22O O (l)(l)

Cu Cu (s)(s) + ZnSO + ZnSO44 (aq)(aq)

Cu(NOCu(NO33))22 (aq)(aq) + 2Ag + 2Ag (s)(s)

Practice:Practice:

6.6. Ca Ca (s)(s) + H + H22O O (l)(l) → ?→ ?

7.7. KClOKClO33 (s)(s) → ? → ?

8.8. MgClMgCl22 (s)(s) + Zn + Zn (s)(s) → ? → ?

9.9. Al Al (s)(s) + HCl + HCl (g)(g) → ? → ?

10.10. Cd Cd (s)(s) + O + O22 (g)(g) → ? → ?

11.11. II2 (s)2 (s) + KF + KF (g)(g) → ? → ?

Complete and balance the Complete and balance the reactions, if they will occur… reactions, if they will occur…

SRSR

DD

SRSR

SRSR

SS

SRSR

Practice:Practice:

6.6. Ca Ca (s)(s) + 2H + 2H22O O (l)(l) → ?→ ?

7.7. 2KClO2KClO33 (s)(s) → ? → ?

8.8. MgClMgCl22 (s)(s) + Zn + Zn (s)(s) → ? → ?

9.9. 2Al 2Al (s)(s) + 6HCl + 6HCl (g)(g) → ? → ?

10.10. 2Cd 2Cd (s)(s) + O + O22 (g)(g) → ? → ?

11.11. II2 (s)2 (s) + KF + KF (g)(g) → ? → ?

Complete and balance the Complete and balance the reactions, if they will occur… reactions, if they will occur…

SRSR

DD

SRSR

SRSR

SS

SRSR

Ca(OH)Ca(OH)22 (aq)(aq) + H + H22 (g)(g)

2KCl 2KCl (s)(s) + 3O + 3O22 (g)(g)

NR NR

2AlCl2AlCl3 (s)3 (s) + 3H + 3H22 (g)(g)

2CdO2CdO (s) (s)

NR NR