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Honors Chemistry
Mr. Fedell
Chapter 8 Note Packet
(teacher edition)
Chapter 8 Problems: see handout!
good figures in the book to look at....
The word on the street is that looking at
illustrations, tables, and figures in the book is a good idea.
8.1
Describing Chemical Reactions
chemical equations describe chemical reactions
reactants
chemical equation:

word equation: say
H2
+
“Hydrogen plus
Cl2
Chlorine

yields

products
2 HCl
Hydrogen Chloride”
other example - creation of sodium chloride
Showing Phases in Chemical Reactions:
gas = (g) or
liquid = (l)
solid = (s)
aqueous (aq)
ex: NaCl (s) = solid sodium chloride
NaCl (aq) = solution of sodium chloride (in water)
H2O (l) - liquid water (not aqueous - redundant)
other symbols:
 = heat
one arrow  = one way reaction
cat = catalyst*
2 arrows ↔ = reversible reaction
= precipitate (solid - only found on products side)
* a substance that speeds up a reaction without being used up in the reaction
Balancing Chemical Equations: truly a trial and error process if there ever was one
Helpful hints:
1. 1 atom at a time
2. Balance atoms that appear only 1X per side first
3. Balance polyatomic ions as whole units
4. Balance diatomic elements last
5. Save H + O for last
if this doesn’t succeed, try doubling everything (particularly with combustion)
Showing Energy Changes in Equations:
1
A + B C + heat ( - ∆H )
A + B + heat  C ( + ∆H ) OR…
exothermic - releases heat – 1 way to represent this:
endothermic - put in heat – 2 ways to represent this:
Interpreting Chemical Equation - what do chemical equations really mean anyway?

H2O
H2
+
O2
(not balanced)
2 H2O

2 H2
+
O2
(equal)
6 atoms
=
4 atoms
+
2 atoms
(equal)
36.0 g
=
4.0 g
+
32.0 g
(equal)
2 molecules
≠
2 molecules
+
1 molecules
(not equal - doesn’t have to)
2 moles
≠
2 moles
+
1 mole
(not equal - doesn’t have to)
8.2
Types of Chemical Reactions
5 types - synthesis, decomposition, combustion, single replacement, double replacement
remember – “First you’ve got to find the right products, then you gotta balance!”
1. Synthesis (direct combination) - needs energy to happen
general formula (element + element):
A
+
B

Ba
+
S

Mg
+
Cl2

Al
+
Cl2

Na
+
O2

AB
2. Decomposition (analysis) - needs energy to happen (usually heat or electricity)
general formula (molecule + element):
FeCl3

HgO

MgSO4
.
7 H2O
AB

A
+
B

(hydrate)
3. Combustion - the reaction of hydrocarbons and oxygen to yield... “when you just say CHO,...”
2
general formula:
ex.
CxHy +
O2

CO2
+
H2O
combustion of CH4, C3H8, C4H10, C2H5OH
4. double replacement – take place in aqueous solution - little energy involved - usually forms
one soluble ionic product (aka - aqueous) and either a ppt, water, or a gas that bubbles out of
water.
general formula
AB
+
CD

AD
+
CB
.
FeCl3 +
NaOH 
H2SO4 +
NaOH 
NH4Cl +
NaOH 
NH3 (g)
+
H2O(l)
+ NaCl(aq)

3. Single Replacement - take place in aqueous solutions and need very little energy
Type 1: positive ions switch
general formula:
AB
+ M
HI
+
Mg

AlCl3
+
Ca

Ca
+
HOH 

MB
+
A
(compound + metal)
Type 2: negative ions switch
general formula:
AB
+ X
NaCl
+
F2

BaS
+
O2

AX +
B (compound + nonmetal)
Hey, some reactions happen and some don’t…
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For synthesis, combustion, and decomposition, we will assume they all happen given
sufficient activation energy (Ea).
For single replacement, use the activity series!
Ca
+
H2O

Al
+
H2O

Al
+
HI

Cu
+
HI

Rules for the single replacement activity series:
1.
2.
3.
4.
Any single element above an element in a compound will replace it.
The top 5 elements react with water.
Metals above H react with acids (molecules that start with H – not water).
The nonmetal reactivity series is FClBr...
For double replacement reactions, use a solubility table and the following rules:
1. If one of the products formed is water, the reaction happens.
2. If a gas is formed, the reaction happens.
3. If an insoluble product forms (I or Ss), the reaction happens (actually a
reaction may happen when two soluble products form, but it doesn’t go to
completion and is not directly observable).
Na2CrO4
+
KCl
FeCl3
+
KOH
Yes! The reaction happens!


NR (both products soluble)
Fe(OH)3(ppt)
+
KCl(aq)
Not balanced yet… “first you gotta find the right products,…”
Note: precipitate symbols include (ppt), (s), and .
NIB - Reactions in Aqueous Solution
Ions in water solutions form aqueous solutions.
4
Ionic compounds are solids.
When you put them in water, they dissociate:
Ex1:
NaBr(s) +
Ex2:
MgCl2(s)

H2O(l)
+
Na+1(aq)
+
Br-1(aq)
2Cl-1(aq)
Mg+2(aq) +
H2O(l)
Also happens with some molecular substances - particularly acids: we call it ionization
Ex3:
HCl(g)
+
Ex4:
H2CrO4(s)
H+1(aq)

H2O(l)
+
H2O(l) 2H+1(aq)
+
Cl-1(aq)
+
CrO4-2(aq)
Writing Ionic Equations
so far we’ve looked at molecular equations
now it’s time for ionic equations - show what happens to the ions in a reaction.
first find products, balance, look up solubilities - remember water is a liquid, write net ionic,
then total ionic, identify spectators.....
Fe(s)
(“molecular” equation)
+
(total ionic)
Fe(s)
+
2H+1(aq)
+
(net ionic)
Fe(s)
+
2H+1(aq)

spectator ion = F-
(“molecular” equation)
(total ionic)
(net ionic)

2HF(aq)
2F-1(aq)
Fe+2(aq)
FeF2(aq)

+
+
Fe+2(aq)
H2(g)
+
2F-1(aq) +
H2(g)
H2(g)
Spectator ions are ions that undergo no change in a chemical reaction.
H2SO4(aq)
+

2NaOH(aq)
Na2SO4(aq)
+
2H(OH)(l)
2H+1(aq) + SO4-2(aq) + 2Na+1(aq) + 2OH-1(aq)  2Na+1(aq) + SO4-2(aq) + 2H(OH)(l)
2H+1(aq)
+
2OH-1(aq) 
spectator ions = SO4-2(aq)
2H(OH)(l)
and
Na+1(aq)
Conservation of Charge - charges must balance in a chemical reaction.
NIB - Solubility Trends
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Cations -
very soluble very insoluble-
Na, K, ammonium
Ag, Pb, Hg, transitions
Anions -
very soluble for monotomics
very insoluble
sulfides
nitrate
FClBr ....
carbonate, hydroxide, phosphate, sulfate
decompose
general trend:
As size decreases, solubility increases.
Some helpful notes on writing phases in chemical reactions:
1. Metals are solids (except
)
2. In single and double replacement reactions, reactants that are compounds are always aqueous.
3. In single and double replacement reactions, products that are compounds should have their
phases identified using a solubility chart (aqueous vs. precipitate)
4. In synthesis and decomposition reactions, ionic compounds are solids.
5. In combustion reactions, the water, CO2, and O2 are gases. The hydrocarbon is hard to tell, but
is usually a liquid after C=5 or higher.
6. Most other covalent compounds are gases.
7. Acids (chemicals starting with hydrogen) are always aqueous.
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