Unit 8
Chemical Reactions
Textbook Chapter 8
Day 1: Review of
Nomenclature (Pg.3 in notes)
Law of Conservation of Mass
Experiment
Matter can neither be created nor
destroyed. Therefore, the amount
of mass I start with will always
equal the amount of mass I get
back in any chemical equation!
2NaOH (aq) + CuSO4 ---- Na2SO4 (aq) + Cu(OH)2 (s)
Today we will be looking at the reaction
of
NaOH with CuSO4.
1. NaOH and CuSO4 are moderately
toxic.
Please be cautious when handling them!
PreLab
1. 2S (s) + 3O2 (g)  2SO3
2. 2HCl + Mg  MgCl2 + H2
In the above reaction, 2.6g
of S reacts with 2.0g O2.
How many grams of SO3
are recovered?
In the above reaction, 5.0g
of HCl react with 2.0g Mg.
3.0g of MgCl2 are
recovered, how many
grams of H2 were lost?
Data Table
Procedure
Mass of cup 1
Mass of cup and NaOH
Mass of NaOH
Mass of cup 2
Mass of cup 2 and CuSO4
Mass of CuSO4
Mass of cup 1 and 2 after mixing
Mass
Homework page 5
Day 2: Nomenclature Review
•
•
•
•
•
aluminum oxide ___________
nitrogen trioxide ___________
copper(II) nitrate
___________
sodium carbonate
________
lead(IV) oxide ________
CHEMICAL REACTIONS
• When 1 or more compounds are reacted to
produce totally new compounds that have
different chemical and physical properties than
they did before.
• A chemical reaction is represented by writing a
chemical equation
– Using chemical formulas, symbols, and
coefficients
• An equation represents, the identities and
relative amounts of what are called reactants
and products in a chemical rxn
– Reactants are the substances you start with
in the reaction
– Products are the results of the reaction
ANATOMY OF A CHEMICAL RXN
Ingredients are
called “reactants”
2H2 + O2
results are
called “products”
2H2O
Coefficient- Reacts
Subscript –
How many
with
# of atoms
“Yields”
or
of that
present
produces
molecule
INDICATIONS OF A CHEM RXN
• To know for certain a chemical rxn has
taken place requires evidence that 1 or
more substances have changed
identity
• Absolute proof of such a change can
only be provided by chemically
analyzing the products.
– However, certain observations can be
made to provide qualitative
indications of a successful chemical
rxn.
– Unexpected change
INDICATIONS OF A CHEM RXN
1) Production of a gas
− Seeing gas bubbles
produced when 2 substances are mixed is
evidence of a reaction
2) Formation of a precipitate
– If a solid appears after
2 solns are mixed, the
solid is called a
precipitate
INDICATIONS OF A CHEM RXN
3) Color change
– Change in color is often
an indication of a
chemical reaction
4) Formation of heat and/or light
– A release of energy as
both heat & light is
strong evidence of a
chemical reaction
SYMBOLS IN REACTIONS
Writing and Balancing Chemical Reactions:
Common Symbols in Reactions
There are other symbols that give scientists additional information about a
reaction.
– These symbols are used to indicate what kinds of reactants and
products are involved, how they react, etc.
SYMBOL
EXPLANATION
+
Separates Reactant from Reactant
or Separates Product from Product

(s)
“Yields” Indicates Result Of Rxn
Separates Reactants from Products
A reactant or product in the solid
state; also used to indicate a
precipitate
SYMBOLS IN REACTIONS
SYMBOL
EXPLANATION
(l)
A reactant or product in the
pure liquid state
(g)
A reactant or product in the gaseous
state
(aq)
A reactant or product in an aqueous
solution (dissolved in water)

cat
Heat is added to the reaction
A catalyst is added to the
reaction
SYMBOLS IN REACTIONS
SYMBOL
MEANING
A gas is produced
A solid is produced
Common Substances in Chemical Reactions
Formula(s) to memorize
Name
Diatomic elements H2, N2,O2, F2,Cl2,Br2,I2
Water
Ammonia
H2O
NH3 (Don’t confuse with
ammonium, NH4+.)
Key Words Used in Describing
Chemical Reactions
Words used to separate reactants
from other reactants.
– “Reacts with”
– “Mixed together”
– “Bubbled through”
Key Words Used in Describing
Chemical Reactions
To separate reactants and
products, you will generally see
one of these words.
*Yield
*Burned
*Produce
*Decompose
*Combusted
*Give
*Form
Class Practice #1
Write the balanced chemical reaction for the following
reaction. Be sure to include all appropriate symbols.
When heated, solid tungsten metal reacts with
oxygen gas to produce solid tungsten(VI) oxide.
W(s) +
O2 (g)


WO3 (s)
2) Solutions of sodium iodide and lead(II)
nitrate are mixed and form the precipitate,
lead(II) iodide and aqueous sodium nitrate.
NaI
(aq)
+ Pb(NO3)2
(aq)
 PbI2 (s) + NaNO3
(aq)
3) When heated, solid aluminum oxide
decomposes to form aluminum metal and
oxygen gas.
Al2O3
(s)

Al (s) +
O2
(g)
Homework page 8
Day 3: Review…again (Page 9)
•
•
•
•
•
Cr2O3
PO2
AlCl3
AgNO3
S2O5
___________
___________
___________
___________
___________
Father of Modern
Chemistry
1743 - 1794
24
First Described the “Law of Conservation of Mass”
Antoine Lavoisier found that the mass of the
reactants and the products are equal, even when the
states of matter change.
HgO
Hg + O2
He started with:
He ended up with:
10g of Mercury
Oxide (HgO)
and 9.3g Mercury…
10 g. = 0.7 + 9.3 g.
...But what
happened to the O2?
Matter is neither created nor destroyed.
25
• Conservation of atoms-the number of each
type of atom on the reactants side of the
chemical equation MUST be equal to the
number of each type of atom on the
products side of the equation.
• Coefficient-represent the number of units
of each substance taking part in the
reaction
• Balanced chemical equation-the same
number of atoms of each element on both
sides of the equation
Four Steps to Balance
Equations:
1. Set up your equation.
2. Count the number of atoms you have on
both sides.
3. Balance by changing the coefficients and
recounting.
4. Start the process again if it still does not
balance.
27
10
Is this balanced?
H2
N2
NH3
Why or Why Not?
Let’s Count the Atoms:
N
N
H
H
H
N
H
H
There are 2
nitrogen atoms
There are 2
hydrogen atoms
1 nitrogen and
3 hydrogen…
Atoms can only bond in certain
ways…and its determined by their
H2
valence electrons
H2
N2
H2
H2
That’s why we can’t
change the subscripts.
N2
H2
N2
N2
N
N2
N
H
H
29
Here is what it means...
Subscripts - Small
#’s below an
element.
H2
Coefficients - Large
#’s in front of the
formulas.
I can’t live
without
you!
2H2
When balancing equations,
we can only change the coefficients!
30
13
Now, back to the
balancing...
1H2
1N2
1NH3
We can only change coefficients
before the symbols.
N
N
H
H
H
N
H
H
1 molecule of
nitrogen
1 molecule of
hydrogen
1 molecule of
ammonia
Do both sides have the same amount of
atoms?
N2 + H 2
NH3
2
N
1
2
H
3
32
Do both sides have the same amount of
atoms?
N2 + 3 H 2
(6)
N 2 + 3 H2
NH3
2
2
N
1
(2)
2
H
3
(6)
2NH3
Then it is a balanced equation.
33
1. Set up your equation.
H2 + O2  H2O
O
H
34
2. Count the number of atoms you have of each
on both sides.
H2 + O2  H2O
2 O 1
2 H 2
35
3. Balance by changing the coefficients and
recounting.
2 H2 + O2  2H2O
2 O 1 (2)
(4) 2 H 2 (4)
How are you going to
make “H” add up to 4?
Need to have at
least 2 “O”
But it changes
the number of
“H”
Is this balanced?
Yes!
36
Let’s try another:
Mg + 2 HCl  H2 + MgCl2
Need to have at
least 2 “Cl”
1 Mg 1
(2) 1 Cl 2
Changing the Cl
changes the
“H”?
(2) 1 H 2
Is this balanced?
Yes!
37
Let’s try another:
Na +2 HCl  NaCl + H2
1 Na 1
In this case, we
will start with
1 Cl 1 hydrogen
since it
is the only one
H
(2) 1
2
unbalanced.
38
But, changing the hydrogen in HCl affects
the number of chlorine atoms.
Na + 2 HCl  2 NaCl + H2
1 Na 1
(2) 1 Cl 1 (2)
(2) 1 H 2
39
Changing the chlorine on the product side affects
the sodium (Na) on the reactants side. So we
must now change sodium as well.
2 Na + 2HCl  2NaCl + H2
(2) 1 Na 1 (2)
(2) 1 Cl 1 (2)
(2) 1 H 2
40
Homework : Pg 10 and 11
Day 4:Oxidation-Reduction Reactions
Page 12
(Synthesis, Decomposition and Single Replacement reactions. )
These are reactions in which electrons are transferred from one
species to another.
• In redox reactions the oxidation number for an
changes
element _________________
in a chemical
reaction.
Oxidation
• __________________
Number: A number
assigned to an element, based on the
distribution of electrons. The same element can
have very different properties in different
oxidation states.
Redox Reactions
0
0
-1
+1
+2
-1
+1
Redox cont.
+1
-1
+2(x1)
+2
+4 (x 1)
+4
+6 (x1)
-6
+6
-8
Oxidation is a reaction
in which there is the
loss of electrons.
Reduction is a reaction in
which there is the gain of
electrons.
0 +1
Ex: Na  Na+1 + e-
0
-1
Ex: Cl2 + 2e-  2Cl-
“LEO the lion says GER”
Losing of Electrons is Oxidation OR
Gaining of Electrons is Reduction
“OIL RIG”
Oxidation Is Loss (of electrons)
Reduction Is Gain (of electrons)
Since oxidation is the loss of electrons and reduction is the gain of electrons,
they must occur simultaneously.
** Any chemical process in which elements undergo changes in oxidation
number is an oxidation – reduction reaction , or redox reaction for short.**
Practice determining whether the following
elements have been oxidized or reduced and
label the reaction.
0
Fe
O
0
0
0
+3 -2
+3
-2
Remember…“OIL RIG”
Lose 3
Gain 2
oxidized
reduced
0 +1 -1
Mg
H
Cl
0
+1
-1
+2 -1
+2
0
-1
0
lose 2
gain 1
neither
oxidized
reduced
neither
Now its YOUR TURN….
Homework!!
Page 14
Day 5: Types of Redox
Reactions
Page 15
1. Synthesis REACTION
(also called Combination or Composition)
• Synthesis means “_put together ”
• 2 or more elements/simple compounds
combine to form 1 compound.
• General form: A +B  AB
• Identifying feature: only one __product__
Analogy: A boy and a girl come to the
dance separately, but end up dancing together.
EX:
2 Mg + O2  2 MgO
EX: The combination of iron and sulfur to form iron (II) sulfide
EX: Burning charcoal
C
(s)
+ O2 (g) → CO2 (g)
Fig. 8-11, p. 214
2. DECOMPOSITION REACTION
• Decomposition means “ break apart ”
• 1 compound is broken down into 2 or
more simpler elements/compounds.
• General form:
AB  A + B
• Identifying feature: only one reactant.
(opposite of Synthesis!)
Analogy: A boy and a girl are a couple, but
they argue and she storms off mad.
Examples:
2 NaCl  2 Na + Cl2
2 KClO3  2 KCl + 3 O2
EX: The electrolysis of water
2H2O(l) → 2H2(g) + O2(g)
Fig. 8-13, p. 215
3. Combustion
Also known as _burning_.
Always follows the same form:
Compound containing C and H (& sometimes O) +
O2
 CO2 + H2O
Note: In a combustion reaction, the
compound always burns in oxygen gas
and always releases
carbon dioxide and water.
During incomplete combustion (a limited amount of
O2), carbon monoxide (CO) is also produced.
Examples: CH4
+ 2 O2  CO2 + 2 H2O
2 C3H6 + 9 O2 
6 CO2 +
6 H2O
**Trick for balancing tough combustion
reactions:**
1) Balance from right to left.
2) Balance the H first by placing a coefficient in front
of the water.
*If that coefficient is ODD,
double it and proceed with balancing C, then O.
* If even, leave it alone and proceed with C, O.
3) Always balance oxygen last!!!
21 O2  _____
14 CO2 + _____
14 7 H2O
2 C7H14 + _____
_____
Homework
pg17
Day 6: Redox continued…
Single Replacement or
Displacement Reactions
4.
Single Replacement (or Displacement)
Reactions
1 element takes the place of another in a compound. “like replaces like”
•
General forms: A + BC  AC + B
(metal replacement)
D + BC  C + BD (halogen replacement)
• Identifying feature: 1 element + 1 compound on
each side of the arrow
NOTE: if the element is a metal, it will replace the metal (cation).
A + BC  C + BA
NOTE: if the element is a nonmetal, it will replace a nonmetal (anion).
Analogy:
A boy and a girl are dancing, but then another
boy “cuts in” and dances with the girl, leaving
the first boy alone. Or a boy and a girl are dancing,
but then another girl “cuts in” and dances with the boy,
leaving the first girl alone. “Like” must replace “like”
Examples:
Metal replacement: 2 Na + CuCl2  2 NaCl + Cu
Halogen replacement: F2 + 2 KCl  2 KF + Cl2
BUT the boy/girl will not always be able to “cut in.”
Sometimes the other boy/girl will not let them!
Rules for Reactions Including: Metals with Metals / Metals with Acids
We must use the activity series to predict whether or not
the replacement will occur.
If an element is more reactive (found higher up in the activity series)
than another element, it WILL replace that element. (Higher element
will only replace something lower, not lower to higher)
Halogen Activity Series (same order as on Periodic Table)
F
Cl
Br
I
(most reactive)
(least reactive)
Examples:
no
Can Al replace Li? ____
yes
Can Cu replace Au? ____
yes
Can Br replace I? ____
no
Can Cl replace F? ____
**Note: This activity series is only used for single replacement reactions.
Single Displacement (or Replacement)
Reactions
pp. 218, 220
Predicting Single
Replacement Reactions
• Must use the
activity series
• Remember a
metal can only
replace
another metal
or hydrogen
Rule #1
Metals replace metals that are lower
than themselves in the activity series
HIGHER
A
LOWER
A
+
LOWER
BX 
B
+ AX
HIGHER
+ BX  no reaction
A and B are metals, and X represents a
negative ion.
Examples
Which reactions will occur?
1. Mg(s) +
AlCl3(aq) 
Yes, the metal in the
compound can trade up!
FeCl2(aq) + Cu(s)  NR
Sodium + Lithium Chloride NR
Silver Nitrate + Zinc  Yes
Predicting the Products
• 3 Mg(s) + 2 AlCl3(aq) 2 Al + 3 MgCl2
• Silver Nitrate + Zinc 
2 AgNO3 + Zn  2Ag +
Zn(NO3)2
Rule #2
Any metal above [H2] will react
with an acid to produce a
compound + H2.
*Put H2 at the end of your
arrow*
Example:
M + HX MX + H2
M = metal
X = negative ion
Examples
Which of these reactions will occur?
– Zn + HCl  YES
– Cu + H2SO4  NO
– Calcium + Phosphoric Acid  YES
Predicting the Products
– Zn + 2HCl  ZnCl2 + H2
– Calcium + Phosphoric Acid 
3 H2
3 Ca +2 H3PO4
Ca3(PO4)2
+
Homework Page 21
Day 7: Redox continued…
Single Replacement
Page 22
Rule #3
Any metal that is
sodium or above will
react with water.
• For these reactions,
it is helpful to think
of water as H-OH.
• M + H2O MOH + H2
Will these reactions occur?
• Na + H2O  YES
• Ca in water. YES
• Cd + H2O  NO
Predict the Products
• Na + H
 NaOH + H2
H-OH
2O
2Na + 2 H2O  2 NaOH + H2
• Calcium metal is placed in
water.
Ca + H-OH  Ca(OH)2 + H2
Ca + 2 H2O  Ca(OH)2 + H2
Rule #4:
Halogens will only replace
other halogens that are
higher in the Activity
Series. Halogens will
NOT replace metals!!!
• There is an activity
series for the halogens.
It is the group on your
periodic table.
Examples
Will these reactions occur?
• F2 + AlCl3  Yes
• Chlorine gas is bubbled
through a solution of
sodium iodide. Yes
• Br2 + KCl  No
Predict the Products
• 3 F2 + 2 AlCl3 3 Cl2 + 2 AlF3
• Chlorine gas is bubbled through a
solution of sodium iodide.
Cl2 + 2NaI  I2
+ 2 NaCl
Experiment of the Types of Reactions
(Chalk Lab)
• You will be using a Bunsen burner, hair
must be pulled back and no sleeves.
• The chalk will be hot, do not touch!
• Please put all waste in the waste
container, NOT DOWN THE SINK!
Day 7 HW pg 24.
Day 8
Precipitate or Double
Replacement Reactions
Understanding solubility!
Page 25
Double Replacement
(or Displacement) Reactions
Ions from 2 ionic compounds switch places.
It is easier to simply remember that the cations (+ ions)
exchange anions (- ions).
General form:
AB + CD  CB + AD
Combine the inner ions and outer ions.
Identifying feature: 2 compounds on each side of
the equation
Analogy: 2 boy-girl pairs are dancing, and they
switch partners.
Example: FeCl2 + Na2CO3  2 NaCl + FeCO3
Note: An acid-base (neutralization) reaction is a special type of double
replacement reaction. It occurs when an acid and a base react to form an
ionic compound (a salt) and water.
pp. 220, 223
Soluble versus Insoluble
• A Soluble Compound…
– Will dissolve.
– Will be labeled as aqueous or (aq) in a
chemical reaction.
• An Insoluble Compound…
– Will NOT dissolve.
– Will be labeled as a solid or (s) in a
chemical reaction.
How to determine if a substance is
soluble?
You will use the solubility chart found
on the back of the Periodic Table of the
Elements.
EXAMPLES

A) Sr(NO3)2
a. Find the anion, or NO3-, on the
chart.
b. If it is in the soluble column, all exceptions
are insoluble. If it is in the insoluble column, all
exceptions are soluble.
Sr(NO3)2 is
soluble
More examples
AgOH 
Insoluble
PbCl2 
Insoluble
Na3PO4
Soluble
Predicting Double
Replacement Reactions
• A precipitate is a solid that forms
when two solutions are mixed.
NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(aq)
A precipitate
will always be a
solid product!
NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)
Fig. 8-18, p. 221
Predicting Double
Replacement Reactions
AX + BY  BY + AX
Your positive ions should switch places!
CuCl2(aq) + Na3PO4(aq) NaCl(aq) +Cu3(PO4)2 (s)
Cu and Na will switch places!
But does a precipitate form?
YES!
Examples
• NaNO3(aq) + KCl(aq) NO REACTION!
• KOH(aq) + Fe(NO3)3(aq) 
3 KOH(aq) + Fe(NO3)3(aq)  Fe(OH)3(s) + 3 KNO3(aq)
• CaCl2(aq) + (NH4)2SO4(aq) 
No Reaction
CaCl2(aq) + (NH4)2SO4(aq) CaSO4(s) + 2NH4Cl(aq)
Day 8 HW page 27.
Compound Formation Lab
ZnCl2
NH4OH
NaOH
CuCl2
FeCl3
PbCl2
NaI