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Chemical Equations & Reactions
Chemical Equations
This equation means:
4 Al(s) + 3 O2(g) 2 Al2O3(s)
4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3
4 Al moles + 3 O2 moles yield 2 moles of Al2O3
or
4 g Al + 3 g O2 yield 2 g Al2O3
4 mol Al@27g/mol 3 mol O2@32g/mol 2 mol Al2O3@102g/mol
108 g + 96 g = 204 g
?
Visualizing a Chemical Reaction
Na + Cl2 NaCl
___ mole Cl2 ___ mole NaCl___ mole Na
2
10 5 10
2
10 5 10
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…
Practice: Balance and Classify1. Ca(OH)2 + HCl CaCl2 + H2O ________________________
2. C2H4 + O2 CO2 + H2O ________________________
3. N2 + O2 N2O
________________________
4. SrCO3 SrO + CO2 ________________________
5. NaI + Br2 NaBr + I2
________________________
6. C2H4O + O2 CO2 + H2O ________________________
7. MgBr2 + (NH4)2SO3 MgSO3 + NH4Br
________________________
8. AgClO3 + (NH4)2Cr2O7 Ag2Cr2O7 + NH4ClO3______________________
9. Cs + H2O CsOH + H2 ________________________
10. Fe + O2 Fe3O4 ________________________
Symbols Used in Chemical Equations
“Yields”; indicates result of reaction
Used to indicate a reversible reaction (equilibrium)
A reactant or product in the solid state; also used to indicate a precipitate
Alternative to (s), but used only to indicate a precipitate
A reactant or product in the liquid state
A reactant or product in an aqueous solution (dissolved in water)
A reactant or product in the gaseous state
(s)
(l)
(aq)
(g)
Additional Symbols Used in Chemical Equations
Alternative to (g), but used only to indicate a gaseous product
Reactants are heated
Pressure at which reaction is carried out, in this case 2 atm
Pressure at which reaction is carried out exceeds normalatmospheric pressure
Temperature at which reaction is carried out, in this case 0 oC
Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction
2 atm
pressure
0 oC
MnO2
D
Signs of Chemical Reactions
There 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
rele
ase
inpu
t
Combustion
O2
General form: CxHx + O2 CO2 H2O
+
+
carbon-hydrogen compound
carbondioxide
C4H10 +
oxygen water
CO2 H2O4 513/2
13 8 102
1. Write a word equation for the reaction
Write a balanced equation for the reaction between chlorineand solid sodium bromide to produce bromine and solid sodium chloride.
2. Write the correct formulas for all reactants and products, (with correct phases of matter)
3. Balance the resulting equation
chlorine + sodium bromide bromine + sodium chloride
Cl2(g) + NaBr(s) Br2(l) + NaCl(s)
Writing Equations Practice
2 2
1) Write a word equation for the reaction
2) Write the correct formulas for all reactants and products
3) Balance the resulting equation
aluminum sulfate + calcium chloride calcium sulfate
Write the balanced equation for the aqueous reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate.
+ aluminum chloride? ?
Al2(SO4)3(aq) + CaCl2(aq) CaSO4(s) + AlCl3 (aq)3 3 2
Oxidation-Reduction Reactions
• “Redox” reactions involve the transfer of electrons (e-)
•Reduction: gain e-
•Oxidation: lose e-
“LEO the lion says, ‘GER’”
“OIL RIG”
• Use oxidation states to keep track of the e-
Leo says Ger
“Lose electron oxidation” Zn 2e- + Zn2+
“Gain electron reduction”2e- + Cu2+ Cu
My name is Leo. Grr-rrrr…
Assigning Oxidation States
Specific rules for assigning Ox #’s • Usually the same charge assigned by the
PT• H is almost always +1 • O is almost always -2 • F is always -1 in compounds• For elements (H2, O2, F2, Ca, K, etc )
the oxidation state always = 0
Some exceptions do exist!
Assigning Oxidation Numbers
• Overall charge = sum of the oxidation states of all atoms in it
Neutral Compounds (e.g. H2O, CO2, CH4)• H2O :
The overall charge is 2(1) + -2 = 0• CO2: What is the oxidation state of C?
Since C + 2 (O) = 0…C + 2(-2) = 0, thus…
• CH4: Is C still +4?H is always +1 To remain neutral… 4(1) + C = 0 C must = - 4
H = +1 and O = -2
C = +4
Assigning Oxidation Numbers
• Charged compounds (e.g. NO3-, CO3
2-)NO3
- or (NO3)- : What is the oxidation # of N?
O is -2, and the overall charge is -1
So N + 3(O) = -1 or N + 3(-2) = -1
N = + 5
(CO3)2-: What is the oxidation # of C?
O is -2, and the overall charge is -2
So C + 3(O) = -2 or C + 3(-2) = -2
C = +4
The oxidation # of ions = charge of ions
Mn3+ has an oxidation # of +3
S2- has an oxidation # of -2
Assigning Oxidation # Practice
Assign oxidation numbers to each atomCl2
Fe2+
ClO3-
ClO4-
IO2-
CrO42-
Fe3(PO4)2
CoSO4
Cl: 0 (element)
Fe: 2+ (ion)
O: 2-, 3(2-) + Cl = 1-…Cl: 5+
O: 2-, 4(2-) + Cl = 1-…Cl: 7+
O: 2-, 2(2-) + I = 1-…I: 3+
O: 2-, 4(2-) + Cr = 2-…Cr: 6+
Fe: 2+ (ion) PO4:3- (ion)….O:2-, 4(2-) + P = 3-, P: 5+
Co: 2+ (ion) SO4:2- (ion)….O:2-, 4(2-) + S = 2-, S: 6+
Assigning Oxidation Numbers Review
• Try these…MnO4-, Cr2O7
2-, C2O42-
• (MnO4)-
O = -2, so [4(-2) + Mn = -1]
Mn = +7
• (Cr2O7)2-
O = -2, so [7(-2) + 2Cr = -2]
2Cr = 12, therefore…
• (C2O4)2-
O = -2, so [2C + 4(-2) = -2]2C = 6, therefore…
Cr = +6
C = +3
Oxidation-Reduction Reactions
• Two separate reactions occurring simultaneously• Oxidation: oxidation # of an atom increases
• e.g. Fe(s) → Fe3+(aq)
• Reduction: oxidation # of an atom is “reduced”• e.g. O2(g) → O2-(aq)
When occurring together…• Fe(s) + O2(g) → Fe3+(aq) + O2-(aq)
• This is the redox reaction responsible for rust!
But, how do we balance this?
(ox # goes from 0 → +3)
(oxidation # goes from 0 → -2)
Balancing by Half-Reactions*in acidic solution
1. Assign oxidation states for each element.
2. Write separate half-reactions for the reduction/oxidation reactions.
3. Balance all the atoms EXCEPT O and H.
4. Balance the oxygen with water (H2O).
5. Balance the hydrogen with hydrogen ions (H+).
6. Balance the charge with electrons.
7. Multiply each half-reaction by an appropriate number to make the electrons equal.
8. Combine both reactions into one and cancel the e -
Balancing by Half-Reactions*in acidic solution
CH3OH (aq) + Cr2O72-(aq) → CH2O(aq) + Cr3+(aq)
1. Assign oxidation states.
C-2H4+O2- + (Cr2
6+O72-)2- → C0H2
+O2- + Cr3+
2. Write separate half-reactions for the reduction and oxidation reactions. (only keep charges that are changing…)
Ox: C-2H4O → C0H2O (C is going from -2 to 0)
Red: (Cr26+O7)2- → Cr3+
(Cr is being reduced from +6 to +3)
3. For each half reaction, balance all atoms EXCEPT O and H.
4. Balance the oxygen by adding water (H2O).
5. Balance the hydrogen by adding hydrogen ions (H+)
6. Balance the charge by adding electrons.…use the oxidation state as a guide
7. Multiply each half-reaction by an appropriate number to make the electrons equal.
8. Add the reactions together and cancel e-/simplify.
Balancing the half reactions…
+ 2H+ + 2e-Ox: C2-H4O → C0H2ORed: (Cr2
6+O7)2- → Cr3+2 + 7H2O14H+ +6e- +
3 ( )
3CH4O → 3CH2O + 6H+ + 6e-
3 CH4O + + Cr2O72- → 3 CH2O + 2 Cr3+ + 7 H2O8 H+
Red: (Cr26+O7)2- → Cr3+
Practice Balancing Redox Reactions
Unbalanced reaction (in acid):
MnO4 + Fe2+ Mn2+ + Fe3+
Balanced Reduction half-reaction:
8H+ + MnO4 + 5e Mn2+ + 4H2O
Balanced Oxidation half-reaction:
Fe2+ Fe3+ + e
Balanced overall reaction:
8H+ + MnO4 + 5Fe2+ Mn2+ + 5Fe3+ + 4H2O
5( )
Balancing by Half-Reactions*in basic solution
1. Assign oxidation states.
2. Write separate half-reactions for the reduction/oxidation reactions.
3. Balance all the atoms EXCEPT O and H.
4. Balance the oxygen by adding water (H2O).
5. Balance the hydrogen by adding H+.
6. Balance the charge by adding electrons.
7. Multiply each half-reaction by an appropriate number to make the electrons equal.
8. Combine both reactions into one and cancel.
9. Add OH- to both sides to cancel out H+ and create H2O. Simplify further, if necessary.
Balancing by Half-Reactions(in basic solution)
Let’s balance a previous example in basic solution
Remember, it is all the same steps up to this point
3CH4O + 8H+ + Cr2O72- → 3CH2O + 2Cr3+ + 7H2O
3CH4O + + Cr2O72- → 3CH2O + 2Cr3+ + 7H2O + 8OH-
3CH4O + H2O + Cr2O72- → 3CH2O + 2Cr3+ + 8OH-
+ 8OH- + 8OH-
8H2O
Practice Balancing Basic Redox Rxns
Unbalanced reaction:ClO + Zn Cl- + Zn2+
Balanced Reduction half-reaction:2e- + 2H+ + ClO- Cl- + H2O
Balanced Oxidation half-reaction: Zn Zn2+ + 2e-
Balanced overall reaction (acidic):
2H+ + ClO + Zn Zn2+ + Cl- + H2O
Balanced overall reaction (basic):
H2O + ClO + Zn Zn2+ + Cl- + 2OH-
Ca
Activity Series
Foiled again:Aluminum is knocked out by Calcium
Element Reactivity
LiRbKBaCaNaMgAlMnZnCrFeNiSnPbH2
CuHgAgPtAu
Halogen Reactivity
F2
Cl2Br2
I2
PrintableVersion
ofActivitySeries
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, aluminum is less reactive than magnesium.
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.
More SR Reactions…
FeCl2 + Cu
MgBr2 + Cl2
“Magic blue-earth”
Zinc in nitric acid
2
A + BC AC + B
General Form
Zn(NO3)2 + H2
Can Fe replace Cu? Yes
LiRbKBaCaNaMgAlMnZnCrFeNiSnPbH2
CuHgAgPtAu
F2
Cl2Br2
I2
Can Zn replace H? Yes
Can Br replace Cl? No
NO REACTION
Fe + CuCl2
Zn + HNO3
MgCl2 + Br2
Activity Series
Double Replacement Reactions
K2CO3 (aq)Potassium carbonate
BaCl2 (aq)Barium chloride
2 KCl (aq)Potassium chloride
BaCO3 (s)Barium carbonate
+ +
Formation of a solid precipitate:
AgNO3(aq) + KCl(aq) KNO3 (aq) + AgCl(s)
TABLE OF SOLUBILITIES IN WATER
aluminum ss s n s n i s s i s d
ammonium s s s s s s s s s s s
barium s s i s i s s s i i d
calcium s s i s s ss s s i ss d
copper (II) s s i s i i n s i s i
iron (II) s s i s n i s s i s i
iron (III) s s n s i i n s i ss d
lead s ss i ss i i ss s i i i
magnesium s s i s s i s s i s d
mercury (I) ss i i i ss n i s i ss i
mercury (II) s ss i s ss i i s i d i
potassium s s s s s s s s s s s
silver ss i i i ss n i s i ss i
sodium s s s s s s s s s s s
zinc s s i s s i s s i s i
acet
ate
brom
ide
carb
onat
e
chlo
ride
chro
mat
e
hydr
oxid
e
iodi
de
nitr
ate
pho
sph
ate
sulfa
te
sulfi
de
i = insolubless = slightly solubles = solubled = decomposesn = not isolated
SOLIDSOLIDAQUEOUS
Legend
Solubility Rules
1. Most nitrates are soluble.
2. Most salts containing Group I ion and ammonium ion, NH4+,
are soluble.
3. Most chloride, bromide, and iodide salts are soluble, except Ag+, Pb2+ and Hg2
2+.
Ohn-Sabatello, Morlan, Knoespel, Fast Track to a 5 Preparing for the AP Chemistry Examination 2006, page 91
4. Most sulfate salts are soluble, except BaSO4, PbSO4, Hg2SO4, and CaSO4.
5. Most hydroxides except Group 1 and Ba(OH)2, Sr(OH)2, and Ca(OH)2 are only slightly soluble.
6. Most sulfides, carbonates, chromates, and phosphates are only slightly soluble.
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
KNO3
Na+K+
potassium chloride + sodium nitrate
KCl(aq)
Using the SOLUBILITY TABLE:sodium chloride is soluble potassium nitrate is soluble
NaNO3 (aq)
K+ Na+ Cl - NO3- Cl- NO3
-
NaCl
sodium chloride potassium nitrate+
(aq) (aq)
Predict if a reaction will occur when you combine aqueous solutions of potassium chloride and sodium nitrate…
If the reaction does occur, write a balanced chemical equation showing it (be sure to include phase notation).
Notice that nothing has really changed because the ions are still dissolved in water!
NR
Pb2+NO3
–
Na+ CI–
Ions in Aqueous Solution Expt.
Pb(NO3)2(s) Pb(NO3)2(aq)
Pb2+(aq) + 2 NO3–(aq)
addwater
NaCI(s)
+ H2O(l)
Dissociation reactions: solids mixed with water dissociate into ions+ H2O(l)
Na+(aq) + CI–(aq)
• Mix them and get…• Balance to get complete ionic equation…• Cancel spectator ions to get net ionic equation…
NaCI(aq)
NO3–
Pb2+
NO3–
NO3–
in solution,aqueous, soluble,dissolved
Na+ CI–
ChemThink
Mix them and get…
Pb2+(aq) + 2 NO31–(aq) + 2 Na1+(aq) + 2 CI–(aq) PbCI2(s) + 2 NO3
1–(aq) + 2 Na1+(aq)
Pb2+(aq) + 2 CI–(aq) PbCI2(s)
Pb(NO3)2(aq) + NaCI(aq)
Balance to get complete ionic equation…separate anything (aq)
Cancel spectator ions to get net ionic equation…
SolubilityChart
Solid (precipitate)
in solution(aqueous)
Pb2+
NO3–
Na+ CI–
NO3–
Na+ CI–
Pb2+
NO3–
Na+
CI–
NO3–
Na+
CI–
PbCI2 + NaNO3(s) (aq) 2 2
Pre-lab:
1. What ions are present in the following solutions?
NaCl(aq) ____________________ AgNO3(aq) ____________________
2. When these solutions are mixed together, a precipitate is seen. What are the new combinations of ions that could have formed the precipitate?
____________________ and ____________________
3. Using the solubility table, which new combination will form a precipitate?
____________________
4. Which new combination will remain in solution?
____________________
5. Write the complete ionic equation for this reaction. Be sure to indicate the correct phase (reaction condition) for each reactant and each product.
6. Write the net ionic equation for this reaction by canceling out spectators. Again, include the phases (reaction conditions).
7. Explain why you would expect no reaction between solutions of KOH(aq) and NaOH(aq).
Na+(aq) Cl-(aq) Ag+(aq) NO3-(aq)
Na+(aq) Cl-(aq)Ag+(aq)NO3-(aq)
Cl-(aq)Ag+(aq)
Na+(aq) NO3-(aq)
AgCl(s)
Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq) + Na+(aq) + NO3
-(aq)AgCl(s)
+ Cl-(aq)Ag+(aq) AgCl(s)
When the cations switch places they end with a hydroxide (no new combination is formed)
Ba2+
OH–
OH–
NO3–
NO3–
Mix together Zn(NO3)2(aq) and Ba(OH)2(aq):
Zn2+(aq) + 2 NO3–(aq) Ba2+(aq) + 2 OH–(aq)
Ba(OH)2(aq)Zn(NO3)2(aq)
Balance to get complete ionic equation…
Zn2+
Zn(NO3)2(aq) + Ba(OH)2(aq) Zn(OH)2(s) + Ba(NO3)2(aq)
Zn2+(aq) + 2 NO3–(aq) + Ba2+(aq) + 2OH–(aq) Zn(OH)2(s) + 2 NO3
–(aq) + Ba2+(aq)
Mix them and get…
Zn2+(aq) + 2 OH–(aq) Zn(OH)2(s)
Cancel spectator ions to get net ionic equation…
SolubilityChart
Separation of Cations
You have a solution containing Fe2+, Cu2+, Ba2+, Ag+
and K+ ions. By what means could you separate these ions from each other?
• In Chem I, we discussed various ways to separate things…• Distillation• Filtration• Centrifugation• Reactivity
Will any of these work to separate aqueous ions?
Separation of CationsFe2+, Cu2+, Ba2+, Ag+, K+ (aq)
+ Cl- (aq)
AgCl(s) Fe2+, Cu2+, Ba2+, K+ (aq)
BaSO4(s) Fe2+, Cu2+, K+ (aq)
CuCrO4(s) Fe2+, K+ (aq)
+ SO42- (aq)
+ CrO42- (aq)
FeS, Fe3(PO4)2 , Fe(OH)2 , or FeCO3(s) K+(aq)
+ S2-, PO43- OH- or
CO32- (aq)
Separation of Cations
Pb2+, Ca2+, Zn2+, NH4+ (aq)
+ CrO42-(aq)
PbCrO4 (s) Ca2+, Zn2+, NH4+ (aq)
CaSO4(s) Zn2+, NH4+ (aq)
NH4+ (aq)
+ SO42- (aq)
ZnCO3, Zn3(PO4)2 , Zn(OH)2, or ZnS(s)
+ CO32-, PO4
3- OH- or S2- (aq)
Try this example on your own…
Summary of Classes of Reactions
Chemical reactions
Double Replacementreactions
Acid-BaseReactions
Oxidation-ReductionReactions
Combustion Reactions
Single Replacementreactions
Synthesis and Decomposition
reactions