Post on 23-Feb-2016
description
Unit 7: Chemical Equations
Chemistry
In a reaction:
atoms are rearranged
AND mass
energy
charge
are conserved
Balancing Chemical Equations
=law of
conservationof mass
same # of atomsof each type on each
side of equation
CH4 + 2 O2 CO2 + 2 H2O
Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms
EX. solid iron reacts with oxygen gas to yieldsolid iron (III) oxide
If all coefficients are 1…
If we change subscripts…
Fe3+ O2– ___Fe(s) + ___O2(g) ___Fe2O3(s)
+
___Fe(s) + ___O2(g) ___Fe2O3(s) 11 1
___Fe2(s) + ___O3(g) ___Fe2O3(s) 11 1
+
But we can’t!!!
Changing a ___________ changes the substance.
To balance, modify only _____________. Right now, _______________ don’t enter intoour “balancing” picture.
subscript
coefficientssuperscripts
___Fe(s) + ___O2(g) ___Fe2O3(s)
+
23
Hint: Start with most complicated substances firstand leave simplest substances for last.
4
2
solid sodium reacts w/oxygento form solid sodium oxide
___O2(g)___Na(s) ___Na2O(s)+
Na+ O2–
+
14
Aqueous aluminum sulfate reacts w/aqueous calciumchloride to form a white precipitate of calcium sulfate.The other compound remains in solution.
Al3+ SO42– Ca2+ Cl–
_ Al2(SO4)3(s)+ _ CaCl2 _ CaSO4 _ AlCl3(aq) (aq) (aq)+1 33 2
1
1
Methane gas (CH4) reacts withoxygen to form carbon dioxidegas and water vapor.
_ CH4(g) + _ O2(g) _ CO2(g) _ H2O(g)+2 1 2
_ CaC2(s) + _ H2O(l) _ C2H2(g) + _ CaO(s)
_ CaSi2 + _ SbI3 _ Si + _ Sb + _ CaI2
_ Al + _ CH3OH _ Al(CH3O)3 + _ H2
1 1 1
3 2 26 3
3262 13
Furnaces burnprimarily methane.
2_ C2H2(g) + _ O2(g) _ CO2(g) + _ H2O(l) ** 5 4 21 2 1
1_ C3H8 + _ O2 _ CO2 + _ H2O ** 5 3 4
1_ C5H12 + _ O2 _ CO2 + _ H2O ** 8 5 6
** = complete combustion (+ O2) of a hydrocarbon (CxHy) yields CO2 and H2O
Write equations for the combustion of C7H16 and C8H18
1_ C7H16 + _ O2 _ CO2 + _ H2O 11 7 8
1_ C8H18 + _ O2 _ CO2 + _ H2O 25 8 92 16 18
Odd # Oxy
Odd # Oxy
Signs of Chemical ReactionsThere are five main signs that indicate a chemical
reaction has taken place:
change in color change in odor production of newgases or vapor
input or releaseof energy
difficult to reverse
releaseinput
Evidence of a chemical reaction:
A reaction has occurred if the chemical and physical
properties of the reactants and products differ.
heatlight
soundgas emittedcolor change
odor
For a reaction to occur,particles of reactantsmust collide, and withsufficient energy
collision theory
activation energy:
Chemical reactions release or absorb energy.
energy needed to start a reaction
exothermic reactions
endothermic reactions
The reaction in an oxy-acetylene torch is exothermic.
Photosynthesis is anendothermic reaction.
Endothermic ReactionEnergy + Reactants Products
Reaction progress
Ene
rgy
Reactants
ProductsActivation Energy
Exothermic ReactionReactants Products + Energy
10 energy = 8 energy + 2 energy
Reactants
Products
Ene
rgy
Energy of reactants
Energy of products
Reaction Progress
Decomposition of Nitrogen Triiodide
2 NI3(s) N2(g) + 3 I2(g)
NI3 I2
N2
catalyst: speeds up reaction w/o being consumed … it lowers the activation energy (Ea)
AEAE
time time
without catalyst with catalyst
Examples: enzymes catalyze biochemical reactions catalytic converters convert CO into CO2
Ener
gy
Reaction Conditions and Terminology
Certain symbols give more info about a reaction(s) = solid (l) = liquid (g) = gas
(aq) = aqueous(dissolved in H2O) NaCl(s) NaCl(aq)
More on aqueous…
“soluble” or “in solution” indicates that a substance is dissolved in water (usually) all acids are aqueous solutions
Other symbols…
means...
Temp. at which we perform rxn. might be given.
The catalyst used might be given.
means ______ is added to the reaction
MgCO3(s) MgO(s) + CO2(g)
C2H4(g) + H2(g) C2H6(g) Pt
C6H5Cl + NaOH C6H5OH + NaCl 400oC
“yields” or “produces”
heat
(i.e., clues about the reaction)
Factors that influencethe rate of a reaction
To make reactionrate increase…
concentration of reactants
particle size
temperature
mechanical mixing
pressure
catalyst use onenature of reactants N/A
Types of Chemical Reactions
Synthesis (combination) reaction
Decomposition reaction
ASingle-replacement reaction
BDouble-replacement reaction
Combustion reaction (of a hydrocarbon)
A + B AB
AB A + B
A + BC AC + B
AB + CD AD + CB
CxHy + O2 CO2 + H2O
Ause activity series to predict products/reactivityBuse solubility chart to predict products/reactivity
element compound elementcompound
All compounds…
Balance and classify the following reactions:
_ F2 _ MgI21 _ I2 + _ MgF2 +1 1 1
Single replacement
_ C3H5N3O94 _ N2 + _ CO26 12 + _ H2O10 + _ O21
Decomposition
1_ C5H12 + _ O2 _ CO2 + _ H2O 8 5 6
Double Replacement?
Combustion
Word EquationsSolid iron reacts with oxygen gas to yield
solidiron(III) oxide.word equation:
balanced equation:
iron
Fe
+ oxygen iron(III) oxide
O2+ Fe3+ O2–
Fe2O324 3
2
Solid sodium reacts w/oxygento form solid sodium oxide.
O2(g) Na(s) Na2O(s)+
Na+ O2–
+
4
Aqueous aluminum sulfate reacts w/aqueous calciumchloride to form a white precipitate of calcium sulfate.The other compound remains in solution.
Al3+ SO42– Ca2+ Cl–
Al2(SO4)3(s)+ CaCl2 CaSO4 AlCl3(aq) (aq) (aq)+33 2
Write a balanced equation (w/rxn conditions)from the following word equations.
Single and Double Replacement Reactions
Double-replacement reaction
CaCO3 + 2 HCl CaCl2 + H2CO3
General form: AB + CD AD + CB
Single-replacement reaction
Mg + CuSO4 MgSO4 + Cu
General form: A + BC AC + B
single-replacement: one elementreplaces another
AB + C A + CB AB + C B + AC
chlorine sodiumbromide
sodiumchloride bromine + +
? aluminum copper (II)sulfate +
_ Cl2 Na+ Br– _ NaBr1 _ Br2 +
Na+ Cl– _ NaCl +2 2 1
Cu2+ SO42–
_ CuSO4_ Al +Al3+ SO4
2– _ Al2(SO4)31 _ Cu+32 3
copper aluminumsulfate +
Ca
Activity Series
Foiled again:Aluminum is knocked out by Calcium
Element Reactivity
LiRbKBaCaNaMgAlMnZnCrFeNiSnPbH2
CuHgAgPtAu
Halogen Reactivity
F2
Cl2Br2
I2
PrintableVersion
ofActivitySeries
Mg + AlCl3
Al + MgCl2
Predict if these reactions will occur
Al + MgCl2
Can magnesium replace aluminum?• Activity Series YES, magnesium is more reactive than aluminum.
2 23 3
Can aluminum replace magnesium?NO, magnesium is less reactive than aluminum.
Therefore, no reaction will occur.
NR (No Reaction)
MgCl2 + Al No reaction
We must determine if the lone element is more reactive than the bonded one… metals replace metals or non-metals replace nonmetals
Order of reactants DOES NOT
determine how they react.
1
How do we know if a reaction will occur?
For single-replacement reactions, use Activity Series.In general, elements above replace elements below.
_ Ba + _ FeSO4
_ Mg + _ Cr(ClO3)3
_ Pb + _ Al2O3
_ NaBr + _ Cl2
_ FeCl3 + _ I2
_ CoBr2 + _ F2
_ Fe + _ BaSO4
_ Cr + _ Mg(ClO3)2
NR
_ NaCl + _ Br2
NR
_ CoF2 + _ Br2
1 1 1
3 2 2 3
2 1
1 1
2 1
1 1
double-replacement:
AD + CBAB + CD
iron (III)chloride + potassium
hydroxide?
Fe3+ Cl– _ FeCl3 +1
K+ OH– _ KOH
Fe3+ OH– K+ Cl– _ KCl_ Fe(OH)3 +3 1 3
iron (III)hydroxide+ potassium
chloride
lead (IV)nitrate + calcium
oxide ?
Pb4+ O2– _ Pb(NO3)4 +1
Ca2+ NO3–
_ CaO _ Ca(NO3)2_ PbO2 +2 1 2Pb4+ O2– Ca2+ NO3
–
lead (IV)oxide + calcium
nitrate
Formation of a solid: AgCl
AgNO3(aq) + KCl(aq) KNO3 (aq) + AgCl(s)
Double Replacement Reactions
precipitate: a solid product that forms in an aqueous solution reaction
When ionic substances have “(aq)” written afterthem, the individual ions have dissociated fromthe ionic crystal and are floating around separately.
Na3PO4(aq) means… 3 Na+(aq) + PO43–(aq)
Sodium phosphate, Na3PO4,(sometimes called “sodium phosphate, tribasic”)
is a cleaning agent and food preservative.
precipitate: a solid product that forms in an aqueous solution reaction
Na2CO3 + Ca(NO3)2 CaCO3 +(aq) (aq)
Na+Ca2+CO3
2–
NO3–
2 (aq)(s)
Na+
NaNO3
NO3–
ppt
clearNa2CO3
solution
clearCa(NO3)2
solution
cloudy solutioncontaining CaCO3(s)
and NaNO3(aq)
“chunks”“sinkies”“floaties”
FeCO3
Na+Fe2+
iron (II) chloride + sodium carbonate
Cl2
Using the SOLUBILITY TABLE:sodium chloride is soluble
iron (II) carbonate is insoluble
CO3
Fe2+
Fe
Na+
Na2
Cl - CO32- Cl- CO3
2-
NaCl
sodium chloride iron (II) carbonate+
(aq) (s)
2FeCl2 Na2CO3 NaCl FeCO3(aq) (s)+ +
Predict if a reaction will occur when you combine aqueous solutions of iron (II) chloride and sodium carbonate…
If the reaction does occur, write a balanced chemical equation showing it (be sure to include phase notation).
(aq) (aq)
Balanced chemical equation
(?)
For double-replacement reactions,reaction will occurif any product is: water a gas a precipitate
driving forces
_ Pb(NO3)2(aq) + _ KI(aq)
_ KOH(aq) + _ H2SO4(aq)
_ FeCl3(aq) + _ Cu(NO3)2(aq)
H+ OH–
Fe3+ Cl– NO3–
Pb2+ NO3– K+ I– Pb2+ NO3
– K+ I–
Check new combinations to decide.
(?)
K+ SO42–
Cu2+
H+ OH– K+ SO42– (?) (?)
Cl– Cu2+
(?)
Fe3+ NO3– (?)
(ppt) (aq)
(aq) (water)
(aq) (aq)
NR
_ K2SO4(aq) + _ H2O(l)
_ PbI2(s) + _ KNO3(aq) 1 2 1 2
2 1 1 2
Ions in Aqueous Solution Pb(NO3)2(s) Pb(NO3)2(aq)
Pb2+(aq) + 2 NO3–(aq)
addwater
dissociation:
Pb2+NO3
–
NO3–
Pb2+
NO3–
NO3–
“splitting into ions”
NaI(s) NaI(aq) Na+(aq) + I–(aq)
Na+ I– Na+ I–add
water
ChemThink
Mix them and get the overall ionic equation…
__Pb2+(aq) + __NO3–(aq) + __Na+(aq) + __I–(aq)
__PbI2(s) + __NO3–(aq) + __Na+(aq) yields
reactants
products
Cancel spectator ions to get net ionic equation… __PbI2(s)1
1 2 2 2
221
Pb2+
NO3–
NO3– Na+ I–
NO3–
NO3–
Na+ I–
Na+
Na+
__Pb2+(aq) + __I–(aq) 1 2
Pb2+I–
I–
Pb2+I–
I–
Pb2+I–
I–
Polymers and Monomers
polymer: a large molecule (often a chain) made of many smaller molecules called monomers
Polymers can be made more rigid if the chains arelinked together by way of a cross-linking agent.
Monomer Polymer
amino acids…………
nucleotides (w/N-bases A,G,C,T/U)…..
styrene………………
PVA………………….
proteins
nucleic acids
polystyrene
“slime”polyvinylalcohol
H–N–C–C–O–HH H O
R