diatomic gases and halogens h, o, n, f, cl occur as diatomic gases covalent bond, attain shared...

Diatomic Gases and Halogens

H, O, N, F, Cl occur as diatomic gasesCovalent bond, attain shared octet

H2 (g)

O2 (g)

N2 (g)

F2(g), Cl2 (g)Remaining halogens also diatomic

Br2(l), I2(s)

Chapter 9 – Chemical Reactions

9.1 Reactions and Equations

9.2 Classifying Chemical Reactions

9.3 Reactions in Aqueous Solutions

Section 9.1 Reactions and Equations

• Recognize evidence of chemical change.

• Represent chemical reactions with equations.

• Balance chemical equations.

• Know which elements occur as diatomic molecules and the states of these elements at room temperature; correctly represent these elements when writing chemical equations which involve them. [not in chapter]

Chemical reactions are represented by balanced chemical equations.

Section 9.1 Reactions and Equations

Key Concepts

• Some 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.

Chemical Reactions

Process by which atoms of one or more substances are rearranged to form different substances

Chemical Equations

Reactants are starting substances

Products are substances formed

reactant 1 + reactant 2 product 1 + product 2

+ separates 2 or more reactants or products

separates reactants from productsRead as “reacts to produce” or “yields”

Parts of Balanced Equation

Subscript - Shows how many atoms of an element are present in a formula unit or molecule of this substance Coefficient – Shows how many formula units or molecules are needed to balance the equation

Chemical Equations

2 Li(s) + 2 H2O(l) 2 LiOH(aq) + H2(g)

(s) identifies solid state(l) identifies liquid state(g) identifies gaseous state(aq) identifies solution in water =

aqueous solution• LiOH(l) not the same as LiOH(aq)

Evidence of Chemical Reactions

Temperature change

Color change

Flame, smoke

Odor

Gas evolution (bubbles)

Appearance of new phase (precipitate)

Word and Skeleton Equations

Word equation

Iron(s) + chlorine(g) iron(III) chloride(s)

“Solid iron and chlorine gas react to produce solid iron(III) chloride”

Skeleton equation• Chemical formulas in place of words

Fe(s) + Cl2(g) FeCl3(s)

Word and Skeleton Equations

Skeleton equation

Solid carbon reacts with solid sulfur to form liquid carbon disulfide

C(s) + S(s) CS2(l)

Note: CS2 is not an ionic compound and ionic compound naming rules do not apply

Practice

Write skeleton equations

Problems 1-3, page 284

Problems 67-72, p 312


Equations and Atoms

Fe(s) + Cl2(g) FeCl3(s)

As written, 1 chlorine atom has been “created” – matter not conserved

+

One iron atom Two chlorine atoms

One iron atom Three chlorine atoms

Balanced Chemical Equations2Fe(s) + 3Cl2(g) 2FeCl3(s)

Both sides have: Two iron atoms Six chlorine atoms

+

Balanced Chemical Equations

2Fe(s) + 3Cl2(g) 2FeCl3(s)

Skeleton equation has been balanced by inserting correct coefficients in front of reactants and/or products

Integers, not written if = 1

Lowest whole number ratio of amounts of reactants and products

Balancing Chemical Equations

Steps (see table 9.2, p 286)

1 – Write skeleton equation

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

Two H atoms

Two Cl atoms

+ One H atomOne Cl atom


2 – Count the atoms of elements in the reactants


2 atoms H

2 atoms Cl


3 – Count the atoms of elements in the products


1 atoms H

1 atoms Cl


4 – Change coefficients to make # of atoms of each elements equal on both sides of the equation

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

2 atoms H (both sides)2 atoms Cl (both sides)


5 – Write the coefficients in their lowest possible whole number ratio


Coefficients as written already in lowest possible ratio


6 – Check your work.

Chemical formulas correctly written?

Number of atoms same on both sides of equation?

All states specified?

Balancing Chemical EquationsFigure 9.6, p 288


When balanced, matter conserved


Two H atoms

Two Cl atoms

+

Two H atomsTwo Cl atoms

Balancing Equation Strategy

Balance elements that occur in only one compound on each side first

Balance free elements last

Balance unchanged polyatomic ions as groups (NO-

3, etc)

Fractional coefficients are acceptable as intermediate result; clear at end by multiplication by common divisor


Combustion of propane

C3H8(g) + O2(g) CO2(g) + H2O(g)

Count atoms on each side

C H O C H O

3 8 2 1 2 3

Not balanced; try to balance C


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

C H O C H O

3 8 2 3 2 7

Not balanced; try to balance H

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

C H O C H O

3 8 2 3 8 10


C3H8(g) + O2(g) 3CO2(g) + 4H2O(g)C H O C H O3 8 2 3 8 10Not balanced; balance oxygen

C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)C H O C H O3 8 10 3 8 10Done

Balancing Practice

NH3(g) + O2(g) N2(g) + H2O(l)

?Balance N: 2 1 1 1

Balance H: 2 1 1 3

Balance O: 2 3/2 1 3

Integers: 4 3 2 6

4NH3(g) + 3O2(g) 2N2(g) + 6H2O(l)

Balancing PracticeC4H10(g) + O2(g) CO2(g) + H2O(g)

Balance C: 1 1 4 1Balance H: 1 1 4 5Balance O: 1 13/2 4 5Integers: 2 13 8 10

2C4H10(g) + 13O2(g)

8CO2(g) + 10H2O(g)

Practice

Note: instruction to “write chemical equation” is understood to mean “write a balanced chemical equation”

Problems 4-6 page 287


Problems 13 page 283

Problems 64, 66, 73-75 page 312

Section 9.2 Classifying Chemical Reactions

• Classify chemical reactions into one or more of 5 possible classes.

• Identify the characteristics of different classes of chemical reactions, including any subclassifications that may apply (redox, formation of hydrogen in acid, etc.).

There are 5 classes of chemical reactions: synthesis, combustion, decomposition, single replacement, and double replacement. The replacement reactions have subclassifications.

• Use the activity series for metals and for halogens to correctly predict if a given pair of reactants will undergo a single replacement reaction.

• Know that the products of the complete combustion of any hydrocarbon or carbohydrate are carbon dioxide and water.

(cont.)



Key Concepts

• 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.

Five Classes of Reactions

Synthesis

Combustion

Decomposition

Single Replacement (4 types)

Double Replacement (3 types)

Synthesis Reactions

Two or more substances react to form a single product A + B C

2Na(s) + Cl2(g) 2 NaCl

CaO(s) + H2O(l) Ca(OH)2(s)

2SO2(g) +O2(g) 2SO3(g)

Combustion Reaction

Oxygen combines with substance

A + O2(g) C or C + DEnergy released rapidly in form of heat & light

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

(Also a synthesis reaction)

Other reactions involve combination with O2(g) but slow process (rusting)

Combustion

C(s) + O2(g) CO2(g)

CH4(g) + 2 O2(g) CO2(g) + 2H2O(g)

Combustion – Special CasesComplete combustion of any hydrocarbon yields CO2 & H2O as products

CH4(g) + 2 O2(g) CO2(g) + 2H2O(g)

2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g)

Same holds true for complete combustion of a carbohydrate (contains CHO only)

C2H7OH = CH3CH2OH ethyl alcohol (ethanol)

4C2H7OH(l) + 13O2(g) 8CO2(g) + 14H2O(g)

Practice

Synthesis & Combustion

Problems 14-17, page 291 *


* Problem 17 has alternate accounting system for aqueous system

Decomposition Reactions

Single compound breaks down into two or more elements or new compounds

AB A + B

Often require source of energy to start• Heat, light, electricity

Decomposition Reactions

NH4NO3(s) N2O(g) + 2H2O(g)

2NaN3(s) 2Na(s) + 3N2(g)

Practice



Problem 87, page 313

Replacement Reactions

Single-Replacement (SR)

Atoms of one element replace atoms of another element

A + BC AC + B

A has replaced B in compound BC

SR reactions are also redox (oxidation reduction) reactions – will examine in more detail in section 19.1

Single-Replacement Reactions

Categories (will discuss each in detail)

Metal replaces H atom in H2O

Metal replaces H atom in HX(aq)

One metal (solid) replaces 2d metal in an aqueous ionic compound

Replacement of nonmetal in compound by another nonmetal (halogens)


Metal replaces H atom in H2O

Think of H2O as HOH

2Li(s) + 2H2O(l) 2LiOH(aq) + H2(g)

Li has replaced H in HOH

Reaction occurs readily for active metals – Li, Na, K, Rb, Ca, etc.

Elemental metal becomes a cation



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

Zn has replaced H in HCl

Reaction occurs readily for more metals than for reaction with water alone

• Depends upon T and acid strength

Elemental metal becomes a cation



M1(s) + M2X(aq) M2(s) + M1X(aq)

M1 = metal # 1 – solid elementalmetal

M2 = metal # 2 – in ionic compound

Replacement only happens when M1 is more active (more reactive) than M2


M1(s) + M2X(aq) M2(s) + M1X(aq)

M1 = metal # 1 – solid elementalmetal

M2 = metal # 2 – in ionic compound

M1 transformed from elemental metal to being a cation in an ionic compound

M2 transformed from cation in an ionic compound to being an elemental metal


One metal (as solid) replaces another metal in a compound dissolved in water

Cu(s) + 2AgNO3(aq)

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

Cu has replaced Ag in AgNO3

Cu more active than Ag (see following)

Cu(s) Cu+2 Ag+ Ag(s)

Note: Product could be CuNO3(aq)

Activity Series for Metals

LithiumRubidniumPotassiumCalciumSodiumMagnesiumAluminumManganeseZinc

IronNickelTinLeadCopperSilverPlatinumGold

Most Active

Least Active


One metal (as solid) replaces another metal in a compound dissolved in water

Ni(s) + NaNO3(aq) NR

NR = no reaction

Nickel is less active than sodium (see following slide)

Activity Series for Metals

LithiumRubidniumPotassiumCalciumSodiumMagnesiumAluminumManganeseZinc

IronNickelTinLeadCopperSilverPlatinumGold

Most Active

Least Active

Practice – from Problem 9.2

Predict products and balance equation

Fe(s) + CuSO4(aq) ???

Is Fe more active than Cu?

YesFe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)

Balanced?

Yes

Fe(s) Fe+2 Cu2+ Cu(s)

Practice – from Problem 9.2Predict products and balance equation

Mg(s) + AlCl3(aq) ???

Is Mg more active than Al?Yes

Mg(s) + AlCl3(aq) Al(s) +MgCl2(aq)Balanced?No

3Mg(s) + 2AlCl3(aq) 2Al(s) + 3MgCl2(aq)

Mg(s) Mg+2 Al3+ Al(s)


Replacement of nonmetal in compound by another nonmetal (halogens)

Most common for halogens

X21 + 2AX2 X2

2 + 2AX1

X1 = halogen number 1 X2 = halogen number 2

Replacement only happens when X1 is more active (more reactive) than X2

X1 elemental halogen becomes anionX2 anion halogen becomes an element


Replacement of one halogen by another halogen

F2(g) + 2NaBr(aq) 2NaF(aq) + Br2(aq)

F has replaced Br in NaBr

Fluorine is more active than bromine (see following slide)

Elemental fluorine has become fluoride

Bromide has become elemental bromine

Activity Series for Halogens

FluorineChlorineBromineIodine

Most Active

Least Active


Replacement of one halogen by another halogen

Br2(l) + MgCl2(aq) ???

Is bromine more active than chlorine?

No

Br2(l) + MgCl2(aq) NR

Activity Series for Halogens

FluorineChlorineBromineIodine

Most Active

Least Active

Practice


Problem 88, page 313

Problems 13-15, pages 980-81

Single-Replacement ReactionsSummary

Active metal replaces H atom in H2O



Replacement of nonmetal in compound by an elemental nonmetal (halogens)

Double-Replacement ReactionsExchange of ions between two compounds in aqueous solution

In example shown above, hydroxide ion and chloride ion have exchanged

Double-Replacement Reactions

One of the products is always:• A gas• Water• Precipitate – solid that comes out of solution

Unlike single replacement reactions, no elemental forms produced – elements start as part of compound and also end that way


2NaOH(aq) + CuCl2(aq) 2NaCl(aq) + Cu(OH)2(s)

Precipitate is product

KCN(aq) + HBr(aq) KBr(aq) + HCN(g)

Gaseous Product

Ca(OH)2(aq) + 2HCl(aq) CaCl2(aq) + 2H2O(l)

Water is product

Double-Replacement ReactionsSteps to determine balanced equation

See table 9.3, p 297

Step 1 – Write reactants in skeleton

Al(NO3)3(aq) + Na2CO3(aq)

Step 2 – Identify anions and cations

Al+3 NO3- Na+ CO3

2-

Step 3 – Swap cations

Na+ NO3- Al+3 CO3

2-


Step 4 – Write formulas for products

Al2(CO3)3(s) NaNO3(aq)

Step 5 – Write complete equation

Al(NO3)3(aq) + Na2 CO3(aq) Al2(CO3)3(s) + NaNO3(aq)

Step 6 – Balance equation

2Al(NO3)3(aq) + 3Na2 CO3(aq) Al2(CO3)3(s) + 6NaNO3(aq)

Practice


Predicting Products of Chemical Reactions Table 9.4, p 298

Section 9.3 Reactions in Aqueous Solutions

• 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.

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


• Know the solubility rules for common cations and anions and use them to predict the occurrence of and formula for a precipitate.

(cont.)


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.

Aqueous Solutions

Water is solvent

Water-soluble substance is the solute

Solutes can be:• Molecules (covalent) that remain intact

Sugar, ethanol• Compounds that form ions

Ionic compounds – NaCl Covalent compounds – HCl, NH3

Aqueous Solutions - Dissociation

NaCl(s) Na+(aq) + Cl-(aq)

NaOH(s) Na+(aq) + OH-(aq)

Ionic compound dissociates into solvated (hydrated) ions that can separate from each other

All soluble ionic compounds do this

Insoluble ionic compounds do not form ions – otherwise, they would dissolve!

Hydration Process for Ionic NaCl

Hydrated Ions

Na Ions Cl Ions

H2O Molecules

Crystal Lattice

Aqueous Solutions

HCl(g) H+(aq) + Cl-(aq)

Despite being primarily a covalent compound, HCl in water dissociates into individual ions that can separate

Net Ionic Equations & Aqueous Reactions

Three types of double replacement reaction have a net ionic equation

Reactions that produce:• A solid (precipitate)• Water (neutralization)• A gas

Reactions Forming a PrecipitateSolubility Rules

For certain common reactions, must learn to predict when a precipitate will form in aqueous solution

Possible to do if know solubility rules – these are not in this chapter but are listed on page 974 (Table R-8)

Are responsible for those rules on the following slide [need to know all for AP]

Ionic Compounds: Solubility in H2OCompounds of alkali metal ions and ammonium ions are soluble

• NaCl(aq), LiOH(aq), (NH4)2CO3(aq)

Nitrates and bicarbonates compounds are soluble

• Mg(NO3)2(aq), NaHCO3(aq)

Carbonates, phosphates, hydroxides, and oxides are insoluble, except for compounds with alkali metals or ammonium ion

• CaCO3(s), AlPO4(s) but Na2CO3(aq)

Ionic Compounds: Solubility in H2OSoluble: Alkali metal, ammonium, nitrate, bicarbonateInsoluble: Carbonate, phosphate, hydroxide, oxide (except with cations above)

Na2S ?

NH4OH ?

Ca3(PO4)2 ?

K2CO3 ?

MgCO3 ?

(NH4)3PO4 ?

Ba(OH)2 ?

Soluble (alkali)

Soluble (ammonium)

Insoluble (phosphate)

Soluble (alkali)

Insoluble (carbonate)

Soluble (ammonium)

Insoluble (hydroxide)

Precipitation Reactions

2NaOH(aq) + CuCl2(aq)

2NaCl(aq) + Cu(OH)2(s)

Solubility rules tell you NaCl must be soluble (alkali metal) and Cu(OH)2 must be insoluble (hydroxide, not alkali or NH4

+)

However, if you forgot hydroxide rule but were told a precipitate forms, know the hydroxide must be the insoluble compound because NaCl can’t be (rule for alkali metal)

Precipitation Reactions2NaOH(aq) + CuCl2(aq)

2NaCl(aq) + Cu(OH)2(s)

Equation does not reveal ionic states

Use complete ionic equation to do this

2Na+(aq) + 2OH-(aq) + Cu2+(aq) + 2Cl-(aq) 2Na+(aq) + 2Cl-(aq) + Cu(OH)2(s)

This does not dissociate (it is not soluble)

Net Ionic Equations

2Na+(aq) + 2OH-(aq) + Cu2+(aq) + 2Cl-(aq) 2Na+(aq) + 2Cl-(aq) + Cu(OH)2(s)

Sodium and chloride ions are spectator ions (don’t participate in reaction)

Dropping them leads to net ionic equation

2OH-(aq) + Cu2+(aq) Cu(OH)2(s)

Practice

Problems 35-39, Page 302

Problems 99, 100 page 313


Reactions That Form Water

H+ and OH- ions can combine to form H2O (covalent)

H+(aq) + OH-(aq) H2O(l)

These reactions also known as acid-base or neutralization reactions

No new phase formed • Already in aqueous phase


HnX type compounds are acids that dissociate into nH+(aq) ions and Xn-

(aq) ions• X=SO4 sulfuric acid

n=2• X=Cl hydrochloric acid

n=1• X=PO4 phosphoric acid

n=3• X=NO3 nitric acid

n=1• X=CO3 carbonic acid

n=2


Me(OH)m type compounds are bases that dissociate into mOH-(aq) ions (hydroxide) and Me+m(aq) metal ions

• Me=Na sodium hydroxide m=1

• Me=K potassium hydroxide m=1

• Me=Ca calcium hydroxidem=2

• Me=Mg magnesium hydroxide m=2


Equation HBr(aq) + NaOH(aq) H2O(l) + NaBr(aq)

Complete ionic equation H+(aq) + Br-(aq) + Na+(aq) + OH-(aq) H2O(l) + Na+(aq) + Br-(aq)

Spectator ions are Na+(aq), Br-(aq)Net ionic equation H+(aq) + OH-(aq) H2O(l)

Practice




Reactions That Form Gases

Carbon dioxide CO2(g)

Hydrogen cyanide HCN(g)

Hydrogen sulfide H2S(g)

Carbon dioxide comes from the decomposition reaction of carbonic acid

H2CO3(aq) CO2(g) + H2O(l)

Reactions That Form GasesEquation 2HI(aq) + Li2S(aq) H2S(g) + 2LiI(aq)

Complete Ionic Equation 2H+(aq) + 2I-(aq) + 2Li+(aq) + S2-(aq)

H2S(g) + 2Li+(aq) + 2I-(aq)

Spectator ions are Li+(aq), I-(aq)

Net ionic equation 2H+(aq) + S2-(aq) H2S(g)

Reactions That Form CO2

Occur when acid added to either a bicarbonate or a carbonate

Equation 1 – double replacement

HCl(aq) + NaHCO3(aq)

H2CO3(aq) + NaCl(aq)

Equation 2 – decomposition

H2CO3(aq) H2O(l) + CO2(g)

Can construct overall equation by combining individual equations

Double-Replacement Followed by Decomposition for CO2


Overall equationHCl(aq) + NaHCO3(aq) + H2CO3(aq)

H2CO3(aq) + NaCl(aq) + H2O(l) + CO2(g)

Cancel substances appearing on both sides of the equationOverall equationHCl(aq) + NaHCO3(aq) NaCl(aq) + H2O(l) + CO2(g)


Overall equation HCl(aq) + NaHCO3(aq) NaCl(aq) + H2O(l) + CO2(g)Complete ionic equation H+(aq) + Cl-(aq) + Na+(aq) + HCO3

-(aq) Na+(aq) + Cl-(aq) + H2O(l) + CO2(g)

Cancel to get net ionic equation

H+(aq) + HCO3-(aq) H2O(l) + CO2(g)

CO2 from Carbonate

Equation 1 – double replacement 2HCl(aq) + Na2CO3(aq)

H2CO3(aq) + 2NaCl(aq)

Equation 2 – decomposition H2CO3(aq) H2O(l) + CO2(g)

Can construct overall equation by combining individual equations

CO2 from Carbonate

Overall equation2HCl(aq) + Na2CO3(aq) + H2CO3(aq)

H2CO3(aq) + 2NaCl(aq) + H2O(l) + CO2(g)

Cancel substances appearing on both sides of the equationOverall equation2HCl(aq) + Na2CO3(aq) 2NaCl(aq) + H2O(l) + CO2(g)

CO2 from Carbonate

Overall equation 2HCl(aq) + Na2CO3(aq) 2NaCl(aq) + H2O(l) + CO2(g)

Complete ionic equation 2H+(aq) + 2Cl-(aq) + 2Na+(aq) + CO3

-(aq) 2Na+(aq) + 2Cl-(aq) + H2O(l) + CO2(g)

Cancel to get net ionic equation

2H+(aq) + CO32-(aq) H2O(l) + CO2(g)

Practice

Problems 45 - 49, page 306

diatomic gases and halogens h, o, n, f, cl occur as diatomic gases covalent bond, attain shared...

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