unit 6 chemical reactions general chemistry spring 2010
TRANSCRIPT
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Unit 6Unit 6Chemical ReactionsChemical Reactions
General ChemistrySpring 2010
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NOMENCLATURE NOMENCLATURE REVIEWREVIEW
Section 1
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IonicIonicBasic Rules
◦These have a cation (+) and an anion (-)◦Usually a metal and a nonmetal◦Sometimes contain polyatomic ion(s)
(back of PT)
◦Pay attention to charges Overall charge on ENTIRE formula has to be
ZERO Use subscripts to add charge to make zero Criss-cross is a shortcut but be careful!
◦Practice this on the next slide
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Basic Ionic FormulaBasic Ionic Formula Give the formulas for the following
compounds w/o PAI
◦ Potassium sulfide
◦ Magnesium oxide Give the formulas w/ PAI
◦ (DON’T CHANGE THE FORMULA)
◦ Aluminum nitrate
◦ Calcium phosphate
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Transition MetalsTransition MetalsIn the name, charge on TM is in ()
◦Ex) Iron (III) chloride
◦Ex) Tin (II) fluoride Use that charge to do criss-cross
To figure out the TM charge do reverse criss-cross. The charge is on ONE TM!
◦Ex) CuO
◦Ex) Cu2O
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Covalent NomenclatureCovalent Nomenclature NO CRISS CROSS!!! NO REDUCE!!! The subscript after the symbol = the prefix in
the name The prefix in the name = the subscript in the
formula (what are these rules?)
1. Ex) NO2
2. Ex) N2O
3. Ex) Sulfur hexafluoride
4. Ex) Triphosphorus pentachloride
Diatomic molecules
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AcidsAcidsEvery acid formula begins with hydrogenThe other half is either a halogen or a
polyatomic ion◦ Halogen? Use “hydro” in name
Ex) HCl
Ex) HF
◦ Polyatomic? Change ending to “-ic” (for this class)
Ex) H3PO4
Ex) H2SO4
# of H’s is the charge on the PAI
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Section 2Section 2Counting Atoms Review
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SubscriptSubscriptIndicates the number present Only applies to the element it’s
withAlCl3
◦One aluminum and three chlorines
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SubscriptsSubscriptsWhen an element has no
subscript◦The implied subscript is ONE
◦Ag1 = Ag
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CoefficientCoefficientAffects anything behind itMultiply everything by the
coefficient3 AlCl3
◦Three aluminums and nine chlorines
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Section 3Section 3Reaction Basics
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Chemical EquationsChemical EquationsThe “sentences” of chemistryShow how elements react with each other
and what compounds they will form
So that’s what happens when
sodium and water mix!!!!
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Parts of a chemical Parts of a chemical EquationEquationReactants
◦Always on the left of the equation◦What the reaction STARTS with
Products◦Always on the right of the equation◦What is produced from the reaction
(made)Yield
◦Arrow◦Where the reaction actually occurs
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Can you show me what you just said???
Mg + O2 MgO
Reactants Products
Yield Sign
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Symbols in Equations (Table Symbols in Equations (Table 11.1)11.1)
Symbol Explanation
+ Used to separate 2 reactions or 2 products
“Yields,” separates reactions from products
Used in place of for reversible rxns
(s) Designates a R or P in the solid state; placed after the formula
(l) A R or P in the liquid state; placed after formula
(g) “ ” in the gas state; “ ”
(aq) Designates an aqueous solution; the substance is dissolved in water; placed after formula
heat Indicates that head is supplied to the rxn
PtA formula written above the yield sign indicates its use as a catalyst (in this example, platinum)
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Section 4Section 4Inventory Reactions
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Law of Conservation of Law of Conservation of MassMassThe reason we balance reactionsMatter is neither created nor
destroyed◦Must account for all elements
Before and after reaction
Antoine-Laurent de Lavoisier
was the first to state this law.
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Reaction AnatomyReaction Anatomy
KClO3 KCl + O2
K 1
Cl 1
O 3
K 1
Cl 1
O 2
Reactant(s) Products
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InventoryInventoryCompare the number of each atom in the
reactants to the products◦ If equal = “balanced reaction”
Abides by the law of conservation of mass◦ If not equal = “not balanced”
Does not abide by the law of conservation of mass; MUST BALANCE
KClO3 KCl + O2
K 1
Cl 1
O 3
K 1
Cl 1
O 2
“Not balanced”
Reactant(s) Products
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Section 5Section 5Balancing Reactions
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BalanceBalance
1. Inventory first2. Locate one element that does not balance3. Add a coefficient to make it balance
◦ NEVER TOUCH A SUBSCRIPT◦ Look to make odd numbers even
4. Re inventory5. Repeat until balanced
KClO3 KCl + O2
K 1
Cl 1
O 3
K 1
Cl 1
O 2
2
2
2
6
32
2
2
6
balanced
It’s best to leave H and O for the end
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BalancingBalancingWhen balancing a chemical
equation you may only change the coefficient (big number in front of the substance)
Balancing example #1:◦ Mg(s) + O2(g) MgO(s)
1 Mg 12 O 1
2 2
2 / / 2 / 2
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Balance Combustion = 2 Balance Combustion = 2 CHORCHOR
Combustion is any reaction with CO2 + H2O for products2…coefficient of 2 in front of big hydrocarbonC…balance carbonsH…balance hydrogenO…balance oxygenR…reduce if possible (divide by a common factor, like 2)
C7H16 + O2 CO2 + H2O 2 14 16 22 1 11 7 8
H C
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Balancing (cont.)Balancing (cont.)
When balancing a chemical equation you may only change the coefficient (big number in front of the substance)
Balancing example #3:◦ NaOH(aq) + H2SO4(aq) Na2SO4(aq) +
HOH(l)
1 Na 21 OH 12 H 11 SO4 1
22
/ 2 / 2
2 / 2 / Count
polyatomic ions as one
piece!
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Practice Problem #1Practice Problem #1
Balance the following reactions:◦ P4(s) + O2(aq) P4O10
◦ Zn + HCl ZnCl2 + H2(g)
◦ Mg(s) + O2(g) MgO(s)
◦ KClO3 KCl + O2(g)
5
2
22
2 2 3
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Section 6Section 6Reaction Types
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Reaction TypesReaction TypesChemical reactions are classified
into 5 different types:◦This makes it easier to see what is
happening in a reaction◦This makes it easier to predict
products in a reaction
Sorting into piles makes it easier to
see the similarities and
differences
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Reaction Types (cont.)Reaction Types (cont.)Five reaction types
◦1) Synthesis (Combination)◦2) Decomposition◦3) Single Replacement◦4) Double Replacement◦5) Combustion
Now let’s look at each type individually
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Please NotePlease NoteThe following reactions are not
balancedThe examples are only used to
show the type of reaction
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Synthesis = S Synthesis = S (Note: The book uses the term “combination;” it’s the (Note: The book uses the term “combination;” it’s the same thingsame thing))
Two or more substances react to form one new compound
Element + element new compoundcompound + compound new
compoundExamples
◦H2 + N2 NH3
◦Mg + O2 MgO (magnesium oxide)
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Decomposition = DDecomposition = D
One compound breaks into two or more simpler products
Compound element/compound + element/compound
Examples◦Na2O Na + O2
◦NH4NO3 N2O + H2O Ammonium nitrate, when heated,
explosively breaks down!
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Single Replacement = SRSingle Replacement = SRElement + compound new
element + new compoundExamples
◦AlCl3 + O2 Al2O3 + Cl2◦H2(SO4) + K K2(SO4) + H2
◦Br2 + NaI NaBr + I2◦Br2 + NaCl No Reaction
Halogen activity decreases as you go down group
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Activity SeriesActivity SeriesWhether one metal
displaces another depends on upon the reactivities of the metals
A reactive metal will replace any metal listed below it on the activity series◦ Ex) iron will displace
copper from a copper compound, but iron does not similarly displace zinc or calcium
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Double Replacement = DRDouble Replacement = DRCompound + compound new
compound + new compoundExamples
◦Na2O + MgBr2 NaBr + MgO
◦H(NO3) + Mg(OH)2 H(OH) + Mg(NO3)2
Which switch? Think about Paula Abdul when you rewrite the formulas!
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Combustion = CCombustion = C
An element or a compound reacts with oxygen, usually producing heat and light
Always involves oxygen as a reactantReaction with CO2 + H2O for productsExamples
◦C6H12O6 + O2 CO2 + H2O
◦2 C8H18 + 25 O2 16 CO2 + 18 H2O
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Visual Review of Types of Visual Review of Types of ReactionsReactions
Single Replacement
Double Replacement
Combustion
Decomposition Synthesis
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Section 7Section 7Predicting Products(p.338-339)
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Synthesis (cont.)Synthesis (cont.)
Steps to predict products:◦ 1. Combine the two
reactants in one product (switchy switchy
◦ 2. Balance
Steps in the Irish Countryside
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Practice Problem #4Practice Problem #4
Predict the product and balance:◦ Mg(s) + O2(g)
◦ Be(s) + Br2(g)
◦ Cs(s) + S2(g)
MgO(s)
BeBr2(s)
Cs2S(s)
22
4 2
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Decomposition (cont.)Decomposition (cont.)
Steps to predict products:◦ 1. Break the one
reactant into two products Don’t forget about
diatomic moleculesH, N, O, F, Cl, Br, I
◦ 2. Balance
Ancient Steps in Cancun, Mexico
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Practice Problem #5Practice Problem #5
Predict the products and balance:◦ MgCl2(s)
◦ FeS(s)
◦ NaI(s)
Mg(s) + Cl2(g)
Fe(s) + S(s)
Na(s) + I2(s)2 2
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Single Replacement (cont.)Single Replacement (cont.)
Steps to predict products:◦ 1. Figure out which metal is
going to replace which other metal
◦ 2. Write the products: One metal is now by itself One metal is now part of a
compound (Switchy Switchy)
◦ 3. Balance
Steps to the House of the Ñusta at Machu Picchu
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Practice Problem #2Practice Problem #2
Predict the products and balance:◦ K(s) + MgS(aq)
◦ Ba(s) + Au(C2H3O2)3(aq)
◦ Zn(s) + HCl(aq)
Mg(s) + K2S(aq)
Au(s) + Ba(C2H3O2)2(aq)
H2(s) + ZnCl2(aq)
2
33 2 2
2
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Double Replacement (cont.)Double Replacement (cont.)
Steps to predict products:◦ 1. Figure out which
metal is going to trade partners with which other metal
◦ 2. Write the products: One metal is now in a
compound with the other anion (switchy switchy)
One metal is now in a compound with the other anion (switchy switchy)
◦ 3. BalanceSteps on a Sand Dune at the
edge of the Gobi Desert
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Practice Problem #3Practice Problem #3
Predict the products and balance:◦ FeS(s) + HCl(aq)
◦ CaCl2(aq) + H2SO4(aq)
◦ NH4I(aq) + AgNO3(aq)
FeCl2(aq) + H2S(g)
HCl(aq) + CaSO4(s)
NH4NO3(aq) + AgI(s)
2
2
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Combustion (cont.)Combustion (cont.)
Steps to predict products:◦ 1. Write CO2 and H2O as
the products◦ 2. Balance…2CHOR
1st balance C 2nd balance H 3rd balance O
Steps to the Lincoln Memorial
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Practice Problem #6Practice Problem #6
Predict the products and balance:◦ C3H8 (g) + O2(g)
◦ C5H12O(s) + O2(g)
◦ C4H10(s) + O2(g)
CO2(g) + H2O(l)
CO2(g) + H2O(l)
CO2(g) + H2O(l)
5 3 4
2 15 10 12
2 13 8 10
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Section 8Section 8Reaction Rates and Equilibrium
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Energy BasicsEnergy BasicsFor a reaction to proceed…
◦Reactants’ bonds must break◦Bonds must reform to make products
Energy is required to break reactants apart (their bonds)
Reactions either gain or lose energy, they never stay the same
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Activation EnergyActivation EnergyBonds must break in order to
reformEnergy required to break bonds
= ACTIVATION ENERGYAll reactions require thisThe activation energy is always
positive
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Energy DiagramEnergy DiagramReactants Products
NaBr + Li(OH) LiBr + Na(OH)
Ene
rgy
in K
ilojo
ules
(kJ
)
Time
Ener
gy o
f rea
ctan
ts
Ene
rgy
of p
rodu
cts
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Energy DiagramEnergy DiagramReactants Products
NaBr + Li(OH) LiBr + Na(OH)
Ene
rgy
in K
ilojo
ules
(kJ
)
Time
Reactants
Products
The difference between the energy of reactants and products =
The total heat or energy of the reaction
OR
ΔΔHH (change in heat) (change in heat)
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Activation EnergyActivation Energy
Reactants
Products (bonds have reformed)
NaBr + Li(OH)
LiBr + Na(OH)
Na+1
Li+1Br-1
(OH) -1
Bonds are brokenBonds are broken
Take
s Ene
rgy
The energy required to break the reactants’ bonds =
ACTIVATION ENERGYACTIVATION ENERGY
Reactants Products
NaBr + Li(OH) LiBr + Na(OH)
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Activated ComplexActivated ComplexE
nerg
y in
Kilo
joul
es (
kJ)
Time
Na+1
Li+1Br-1
(OH) -1
Bonds are brokenBonds are broken
Reactants Products
NaBr + Li(OH) LiBr + Na(OH)
Reactants
Products
The point at which all bonds have been broken and products begin to reform =
ACTIVATED COMPLEXACTIVATED COMPLEX
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SummarySummaryE
nerg
y in
Kilo
joul
es (
kJ)
Time
Reactants Products
NaBr + Li(OH) LiBr + Na(OH)
Reactants
Products
Activated Complex
Activation Energy
Total heat of reaction or ΔH
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Rates of ReactionRates of ReactionWays to make reactions happen
faster:◦Make chemicals at higher
concentration◦Increase the temperature◦Make the particles smaller◦Add a catalyst
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Rates of Reactions (cont.)Rates of Reactions (cont.)Catalysts lower the activation energy
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Heats of ReactionHeats of Reaction
Reactions can either…◦Give off heat
Exothermic The energy level at the end of the reaction is
lower than the energy level at the beginning of the reaction
Therefore, the change in heat (∆H) is negative◦Take in heat
Endothermic The energy level at the end of the reaction is
higher than the energy level at the beginning of the reaction
Therefore, the change in heat (∆H) is positive
Feels Hot
Feels Cold
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Exothermic Reaction◦ Reaction loses heat◦ ΔH value is always
negative
Endothermic Reaction◦ Reaction gains heat◦ ΔH value is always
positive
energy
time
energy
time
Exo vs Endothermic Reactions
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Bond Formation (cont.)Bond Formation (cont.)
Example #1◦ Endo or
exothermic?
◦ Energy of the Activated complex?
◦ ∆H?
Reactants (500 kJ)
Products (200 kJ)
Act. Energy (150 kJ) Exothermic
650 kJ
-300 kJ
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Bond Formation (cont.)Bond Formation (cont.)
Example #2◦ Endo or exothermic?
◦ Activation energy?
◦ Energy of products?
Endothermic
750 kJ
600 kJ
Reactants (200 kJ)
∆H (400 kJ)
Activated Complex (950 kJ)