1. Chemistry
Unit 7:
Chemical Equations

2. = In a reaction: atoms are rearranged Balancing Chemical Equations
mass
AND
energy
are conserved
charge
Balancing Chemical Equations
law of
conservation
of mass
same # of atoms
of each type on each
side of equation =

3. CH4 + 2 O2  CO2 + 2 H2O Reactants Products 1 C atom 1 C atom
4 H atoms H atoms
4 O atoms O atoms

4. EX. solid iron reacts with oxygen gas to yield solid iron (III) oxide
Fe3+
O2–
___Fe(s) +
___O2(g)
___Fe2O3(s)
If all coefficients are 1…
___Fe(s) 1 +
___O2(g) 1
___Fe2O3(s) 1 +
We discussed abbreviations for phases of matter in Unit 2 and we will revisit this topic later in this unit. For right now we can just reiterate that it is conventional to include phases in equations.
If we change subscripts…
But we can’t!!!
___Fe2(s) +
___O3(g)
___Fe2O3(s) 1 +

5. Changing a ___________ changes the substance.
subscript
To balance, modify only _____________.
coefficients
Right now, _______________ don’t enter into
our “balancing” picture.
superscripts
___Fe(s) +
___O2(g)
___Fe2O3(s) 4 3 2 +
Hint: Start with most complicated substances first
and leave simplest substances for last.

6. solid sodium reacts w/oxygen to form solid sodium oxide Na+ O2–
___Na(s) 4 +
___O2(g) 1
___Na2O(s) 2 +
Aqueous aluminum sulfate reacts w/aqueous calcium
chloride to form a white precipitate of calcium sulfate.
The other compound remains in solution.
Al3+
SO42–
Ca2+
Cl– 1
_ Al2(SO4)3 3 3 2
(aq) +
_ CaCl2
(aq)
_ CaSO4
(s) +
_ AlCl3
(aq)

7. Furnaces burn
primarily methane.
Methane gas (CH4) reacts with
oxygen to form carbon dioxide
gas and water vapor. 1
_ CH4(g) +
_ O2(g) 2 1
_ CO2(g) +
_ H2O(g) 2
_ CaC2(s) + _ H2O(l) _ C2H2(g) + _ CaO(s) 1 1 1 1
_ CaSi2 + _ SbI _ Si + _ Sb + _ CaI2 3 2 6 2 3 2
_ Al + _ CH3OH _ Al(CH3O)3 + _ H2 3 6 1 2 3

8. _ C2H2(g) + _ O2(g) _ CO2(g) + _ H2O(l) 2 1 5 4 2 1 2 Odd # Oxy **
_ C3H8 + _ O _ CO2 + _ H2O 1 5 3 4 **
_ C5H12 + _ O _ CO2 + _ H2O 1 8 5 6
** =
complete combustion (+ O2) of a hydrocarbon (CxHy) yields CO2 and H2O
Write equations for the combustion of C7H16 and C8H18
Introduction of definition of combustion reaction based on reactants and products (Fri 1/11). Can re-use this slide if we don’t get this far.
_ C7H16 + _ O _ CO2 + _ H2O 1 11 7 8
_ C8H18 + _ O _ CO2 + _ H2O 2 1 25 16 8 18 9
Odd # Oxy

9. Signs of Chemical Reactions
There are five main signs that indicate a chemical reaction has taken place:
release
input
Start on Monday (1/14).
change in color
change in odor
production of new
gases or vapor
input or release
of energy
difficult to reverse

10. Evidence of a chemical reaction:
odor
light
heat
gas emitted
sound
color change
A reaction has occurred if the chemical and physical
properties of the reactants and products differ.
For a reaction to occur,
particles of reactants
must collide, and with
sufficient energy
collision theory

11. acetylene torch is exothermic.
activation energy:
energy needed to start a reaction
Chemical reactions release or absorb energy.
exothermic
reactions
endothermic
reactions
The reaction in an oxy-
acetylene torch is exothermic.
Photosynthesis is an
endothermic reaction.

12. Energy + Reactants  Products
Endothermic Reaction
Energy + Reactants  Products
Activation
Energy
Products
Energy
Reactants
Reaction progress

13. Exothermic Reaction 10 energy = 8 energy + 2 energy
Reactants  Products + Energy
10 energy = energy energy
Energy of reactants
Energy of products
Energy
Reactants
Products
Reaction Progress

14. Decomposition of Nitrogen Triiodide
Molecules store energy (chemical potential energy) in the bonds that hold them together. When the bonds are broken, energy is released.
2 NI3(s) N2(g) I2(g)

16. catalyst: speeds up reaction w/o being consumed…
it lowers the activation energy (Ea)
without catalyst
with catalyst AE AE
Energy
time
time
Examples:
enzymes catalyze biochemical reactions
catalytic converters convert CO into CO2

17. 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)
Already seen these a couple of times. Review.
More on aqueous…
“soluble” or “in solution” indicates that a
substance is dissolved in water (usually)
all acids are aqueous solutions

18. (i.e., clues about the reaction)
Other symbols…
(i.e., clues about the reaction)
means...
“yields” or “produces”
means ______ is added to the reaction
heat
MgCO3(s) MgO(s) + CO2(g)
Temp. at which we perform rxn. might be given.
400oC
C6H5Cl + NaOH C6H5OH + NaCl
The catalyst used might be given.
C2H4(g) + H2(g) C2H6(g) Pt

19. Factors that influence
the rate of a reaction
To make reaction
rate increase…
concentration of reactants
particle size
temperature
mechanical mixing
pressure
catalyst
use one
nature of reactants
N/A

20. Types of Chemical Reactions
Synthesis (combination) reaction
A B  AB
Decomposition reaction
AB  A + B
ASingle-replacement reaction
A BC  AC + B
element
compound
compound
element
BDouble-replacement reaction
AB CD  AD + CB
All compounds…
Combustion reaction
(of a hydrocarbon)
CxHy O2  CO2 + H2O
Objective:
To classify a chemical reaction as one of the following types: combination (synthesis), decomposition, single replacement, double replacement, or neutralization.
Ause activity series to predict products/reactivity
Buse solubility chart to predict products/reactivity

21. Classifying Reactions
four types
synthesis: simpler substances combine to form
more complex substances
A + B AB AB + C ABC A + B + C ABC
oxygen + rhombic sulfur sulfur dioxide
__ O2 8 +
__ S8 1
__ SO2 8
sodium + chlorine gas sodium chloride
__ Na 2 +
__ Cl2 1
__ NaCl 2

22. decomposition: complex substances are broken
down into simpler ones
AB A + B ABC AB + C ABC A + B + C
lithium chlorate lithium chloride + oxygen
Li+
ClO3–
Li+
Cl–
_ LiClO3 2 2
_ LiCl
+ _ O2 3
water hydrogen gas + oxygen gas 2
_ H2O 2
_ H2
+ _ O2 1

23. single-replacement: one element replaces another AB + C A + CB
AB + C B + AC
chlorine
sodium
bromide
chloride
bromine +
Na+
Br–
Na+
Cl– 1
_ Cl2 2
_ NaBr 2
_ NaCl 1 + +
_ Br2
aluminum
copper (II)
sulfate +
copper
aluminum
sulfate + ?
Cu2+
SO42–
Al3+
SO42–
_ Al 2 + 3
_ CuSO4
_ Al2(SO4)3 1 + 3
_ Cu

24. double-replacement: AB + CD AD + CB iron (III) chloride + potassium
hydroxide
iron (III)
hydroxide +
potassium
chloride ?
Fe3+
Cl– K+
OH–
Fe3+
OH– K+
Cl– 1
_ FeCl3 + 3
_ KOH 1
_ Fe(OH)3 + 3
_ KCl
Worth asking what classification would we give to combustion reactions. Answer: depends – most would probably be called double replacement (where CD = O2), combustion of H2 or C would be synthesis.
lead (IV)
nitrate +
calcium
oxide
lead (IV)
oxide +
calcium
nitrate ?
Pb4+
NO3–
Ca2+
O2–
Pb4+
O2–
Ca2+
NO3–
_ Pb(NO3)4 1 + 2
_ CaO 1
_ PbO2 + 2
_ Ca(NO3)2

25. Balance and classify the following reactions:1
_ F2 1
_ MgI2
_ MgF2 1 1 + +
_ I2
Single replacement 10 1
_ C3H5N3O9 4
_ N2 6
+ _ CO2 12
+ _ H2O
+ _ O2
Decomposition
_ C5H12 + _ O _ CO2 + _ H2O 1 8 5 6
Double Replacement?
Combustion

26. Word Equations
Solid iron reacts with oxygen gas to yield solid
iron(III) oxide.
word equation:
iron +
oxygen 
iron(III) oxide
Fe3+
O2–
balanced equation: 4 Fe + 3 O2  2
Fe2O3

27. Write a balanced equation (w/rxn conditions)
from the following word equations.
Solid sodium reacts w/oxygen
to form solid sodium oxide.
Na+
O2–
Na(s) 4 +
O2(g)
Na2O(s) 2 +
Aqueous aluminum sulfate reacts w/aqueous calcium
chloride to form a white precipitate of calcium sulfate.
The other compound remains in solution.
Al3+
SO42–
Ca2+
Cl–
Al2(SO4)3
(aq) + 3
CaCl2
(aq)
CaSO4 3
(s) + 2
AlCl3
(aq)

28. Single and Double Replacement Reactions
Single-replacement reaction
Mg CuSO4  MgSO Cu
General form:
A BC  AC B
Double-replacement reaction
CaCO HCl  CaCl H2CO3
General form:
AB CD  AD CB

29. single-replacement: one element replaces another AB + C A + CB
AB + C B + AC
chlorine
sodium
bromide
chloride
bromine +
Na+
Br–
Na+
Cl– 1
_ Cl2 2
_ NaBr 2
_ NaCl 1 + +
_ Br2
aluminum
copper (II)
sulfate +
copper
aluminum
sulfate + ?
Cu2+
SO42–
Al3+
SO42–
_ Al 2 + 3
_ CuSO4
_ Al2(SO4)3 1 + 3
_ Cu

30. Activity Series Foiled again: Aluminum is knocked out by Calcium
Printable
Version of
Activity
Series
Element Reactivity Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H2 Cu Hg Ag Pt Au Ca
Foiled again:
Aluminum is knocked out by Calcium
Halogen Reactivity F2
Cl2
Br2 I2
Objectives:
To explain the concept of an activity series for metals.
To predict whether a single-replacement reaction occurs by referring to the activity series.

31. Predict if these reactions will occur3
Mg AlCl3 2 2
Al MgCl2 3
Can magnesium replace aluminum?
Activity Series
YES, magnesium is more reactive than aluminum.
Al MgCl2
NR (No Reaction)
Can aluminum replace magnesium?
Therefore, no reaction will occur.
NO, magnesium is less reactive than aluminum.
Order of reactants
DOES NOT
determine how
they react.
MgCl 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

32. How do we know if a reaction will occur?
For single-replacement reactions, use Activity Series.
In general, elements above replace elements below. 1
_ Ba + _ FeSO4 1 1
_ Fe + _ BaSO4 1 3
_ Mg + _ Cr(ClO3)3 2 2
_ Cr + _ Mg(ClO3)2 3
_ Pb + _ Al2O3 NR 2
_ NaBr + _ Cl2 1
_ NaCl + _ Br2 2 1
_ FeCl3 + _ I2 NR 1
_ CoBr2 + _ F2 1 1
_ CoF2 + _ Br2 1

33. double-replacement: AB + CD AD + CB iron (III) chloride + potassium
hydroxide
iron (III)
hydroxide +
potassium
chloride ?
Fe3+
Cl– K+
OH–
Fe3+
OH– K+
Cl– 1
_ FeCl3 + 3
_ KOH 1
_ Fe(OH)3 + 3
_ KCl
Worth asking what classification would we give to combustion reactions. Answer: depends – most would probably be called double replacement (where CD = O2), combustion of H2 or C would be synthesis.
lead (IV)
nitrate +
calcium
oxide
lead (IV)
oxide +
calcium
nitrate ?
Pb4+
NO3–
Ca2+
O2–
Pb4+
O2–
Ca2+
NO3–
_ Pb(NO3)4 1 + 2
_ CaO 1
_ PbO2 + 2
_ Ca(NO3)2

34. Formation of a solid: AgCl
Double Replacement Reactions
Formation of a solid: AgCl
AgNO3(aq) + KCl(aq)  KNO3 (aq) + AgCl(s)

35. precipitate: a solid product that forms in an
aqueous solution reaction
When ionic substances have “(aq)” written after
them, the individual ions have dissociated from
the 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.

36. precipitate: a solid product that forms in an
aqueous solution reaction
Na2CO Ca(NO3)2
(aq)
(aq)
CaCO
(s) 2
NaNO3
(aq)
“chunks”
NO3–
Na+
“sinkies”
CO32–
Ca2+
NO3–
Na+
“floaties”
ppt
clear
Na2CO3
solution
clear
Ca(NO3)2
solution
cloudy solution
containing CaCO3(s)
and NaNO3(aq)

37. 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).
Balanced chemical equation
iron (II) chloride sodium carbonate
sodium chloride +
iron (II) carbonate
Fe2+
Cl -
Na+
CO32-
Fe2+
Cl-
Na+
CO32-
Cl2 Fe
CO3
Na2
NaCl
FeCO3
(aq)
(s)
Using the SOLUBILITY TABLE:
sodium chloride is soluble
iron (II) carbonate is insoluble
FeCl2
Na2CO3
NaCl
FeCO3
(aq)
(s) + 2
(aq)
(aq)

38. NR For double-replacement reactions, reaction will occur
if any product is:
water a gas a precipitate
driving forces
Check new combinations to decide.
_ Pb(NO3)2(aq) + _ KI(aq) 1 2
_ PbI2(s) + _ KNO3(aq) 1 2
Pb2+
NO3– K+ I–
Pb2+ I–
(?) K+
NO3–
(?)
(ppt)
(aq) 2
_ KOH(aq) + _ H2SO4(aq) 1 1
_ K2SO4(aq) + _ H2O(l) 2 K+
OH– H+
SO42– K+
SO42–
(?) H+
OH–
(?)
(aq)
(water)
_ FeCl3(aq) + _ Cu(NO3)2(aq) NR
Fe3+
NO3–
(?)
Cl–
Cu2+
(?)
Fe3+
Cl–
Cu2+
NO3–
(aq)
(aq)

39. Ions in Aqueous Solution
Pb(NO3)2(s)
Pb(NO3)2(aq)
Pb2+(aq) NO3–(aq)
Pb2+
NO3–
Pb2+
NO3–
add
water
dissociation:
“splitting into ions”
NaI(s)
NaI(aq)
Na+(aq) + I–(aq)
add
water
Na+ I–
Na+ I–
ChemThink

40. Mix them and get the overall ionic equation…
Pb2+
Na+ I–
NO3–
NO3–
Na+ I–
reactants
__Pb2+(aq) + __NO3–(aq) + __Na+(aq) + __I–(aq) 1 2 2 2
yields
__PbI2(s) 1
+ __NO3–(aq) + __Na+(aq) 2 2
Na+
products
Pb2+ I–
NO3–
Na+
NO3–
Cancel spectator ions to get net ionic equation…
__Pb2+(aq) + __I–(aq) 1 2
__PbI2(s) 1
Pb2+ I–
Pb2+ I– I–

41. Mix together Zn(NO3)2(aq) and Ba(OH)2(aq):
clear Zn(NO3)2 solution
clear Ba(OH)2 solution
Zn(NO3)2(aq)
Ba(OH)2(aq)
Zn2+(aq) NO3–(aq)
Ba2+(aq) OH–(aq)
Zn2+
NO3–
Ba2+
OH–

42. Mix them and get the overall ionic equation…
Zn2+
Ba2+
OH–
NO3–
NO3–
OH–
reactants
__Zn2+(aq) + __NO3–(aq) + __Ba2+(aq) + __OH–(aq) 1 2 1 2
yields
__Zn(OH)2(s) 1
+ __NO3–(aq) + __Ba2+(aq) 2 1
Ba2+
products
Zn2+
OH–
NO3–
NO3–
Cancel spectator ions to get net ionic equation…
__Zn2+(aq) + __OH–(aq) 1 2
__Zn(OH)2(s) 1
Zn2+
OH–
Zn2+
OH–
OH–

43. 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 are
linked together by way of a cross-linking agent.

44. Monomer
Polymer
H–N–C–C–O–H
H H O R
amino acids…………
proteins
nucleotides (w/N-
bases A,G,C,T/U)…..
nucleic acids
styrene………………
polystyrene
PVA………………….
“slime”
polyvinyl
alcohol

45. Quantitative Relationships in Chemical Equations
4 Na(s) O2(g) Na2O(s)
Particles
4 atoms
1 m’cule
2 m’cules
Moles
4 mol
1 mol
2 mol
Grams
4 g
1 g
2 g **
Coefficients of a balanced equation represent
# of particles OR # of moles,
but NOT # of grams.

46. Use coeff. from bal. eq. to go
SUBSTANCE “A”
SUBSTANCE “B”
Use coeff. from bal. eq. to go
from “moles of A”
to “moles of B”
Part.
Vol.
Mass
MOL
(known)
(unknown)

47. ( ) ( ) ( ) 4 Na(s) + O2(g) 2 Na2O(s) Na2O Na Na2O Na O2
How many moles oxygen will react with 16.8 moles sodium? ( )
1 mol O2
16.8 mol Na
= mol O2
4 mol Na
How many moles sodium oxide are produced from
87.2 moles sodium? ( )
2 mol Na2O
87.2 mol Na
= mol Na2O
4 mol Na
How many moles sodium are required
to produce moles sodium oxide? ( )
4 mol Na
0.736 mol Na2O
= mol Na
2 mol Na2O