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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
Problems 1-2, page 980
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
Balancing Chemical Equations
2 – Count the atoms of elements in the reactants
H2(g) + Cl2(g) HCl(g)
2 atoms H
2 atoms Cl
Balancing Chemical Equations
3 – Count the atoms of elements in the products
H2(g) + Cl2(g) HCl(g)
1 atoms H
1 atoms Cl
Balancing Chemical Equations
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)
Balancing Chemical Equations
5 – Write the coefficients in their lowest possible whole number ratio
H2(g) + Cl2(g) 2HCl(g)
Coefficients as written already in lowest possible ratio
Balancing Chemical Equations
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
Balancing Chemical Equations
When balanced, matter conserved
H2(g) + Cl2(g) 2HCl(g)
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
Balancing Chemical Equations
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
Balancing Chemical Equations
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
Balancing Chemical Equations
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 3-8, page 980
Problems 13 page 283
Problems 64, 66, 73-75 page 312
Chapter 9 – Chemical Reactions
9.1 Reactions and Equations
9.2 Classifying Chemical Reactions
9.3 Reactions in Aqueous Solutions
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.)
Section 9.2 Classifying Chemical Reactions
Section 9.2 Classifying Chemical Reactions
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 *
Problems 84-86 page 313
* 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
Problems 18-20 page 292
Problems 11-12 page 980
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)
Single-Replacement Reactions
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
Single-Replacement Reactions
Metal replaces H atom in HX(aq)
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
Single-Replacement Reactions
One metal (solid) replaces 2d metal in an aqueous ionic compound
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
Single-Replacement Reactions
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
Single-Replacement Reactions
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
Single-Replacement Reactions
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)
Single-Replacement Reactions
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
Single-Replacement Reactions
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
Single-Replacement Reactions
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
Problems 21-24, page 295
Problem 88, page 313
Problems 13-15, pages 980-81
Single-Replacement ReactionsSummary
Active 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 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
Double-Replacement Reactions
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-
Double-Replacement Reactions
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
Problems 25-28, page 297
Predicting Products of Chemical Reactions Table 9.4, p 298
Chapter 9 – Chemical Reactions
9.1 Reactions and Equations
9.2 Classifying Chemical Reactions
9.3 Reactions in Aqueous Solutions
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.
Section 9.3 Reactions in Aqueous Solutions
• Know the solubility rules for common cations and anions and use them to predict the occurrence of and formula for a precipitate.
(cont.)
Section 9.3 Reactions in Aqueous Solutions
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
Problems 18-19, page 981
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
Reactions That Form Water
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
Reactions That Form Water
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
Reactions That Form Water
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
Problems 40-44, page 304
Problems 100-102, page 313
Problems 20-21, page 981
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
Reactions That Form 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)
Reactions That Form CO2
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