Transcript Chapter 11

Chemical Reactions
1
Solutions
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2
Solutions are defined
as homogeneous
mixtures of two or
more pure
substances.
The solvent is present
in greatest abundance.
All other substances
are solutes.
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Parts of Solutions
Solution- homogeneous mixture.
 Solute- what gets dissolved.
 Solvent- what does the dissolving.
 Soluble- Can be dissolved.
 Miscible- liquids dissolve in each
other.
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Aqueous solutions
Dissolved in water.
 Water is a good solvent
because the molecules are
polar.
 The oxygen atoms have a
partial negative charge.
 The hydrogen atoms have a
partial positive charge.
 The angle is 105ºC.
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4
Hydration
The process in which an ion is
surrounded by water molecules
arranged in a specific manner
 Ions have charges and are attracted
to the opposite charges on the water
molecules.
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How Ionic solids dissolve
Click here for
Animation
H
H
H
H
H
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Dissociation
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When an ionic
substance dissolves
in water, the solvent
pulls the individual
ions from the crystal
and solvates them.
This process is
called dissociation.
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Dissociation

An electrolyte is a
substances that
dissociates into
ions when dissolved
in water.
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Electrolytes
Electricity is moving charges.
 The ions that are dissolved can
move.
 Solutions of ionic compounds can
conduct electricity.
 Electrolytes.
 Solutions are classified three ways.
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Types of solutions
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Strong electrolytes- completely dissociate
(fall apart into ions).
– Many ions- Conduct well.
Weak electrolytes- Partially fall apart into
ions.
– Few ions -Conduct electricity slightly.
Non-electrolytes- Don’t fall apart.
– No ions- Don’t conduct.
Electrolytes
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An electrolyte is a
substances that
dissociates into
ions when dissolved
in water.
A nonelectrolyte
may dissolve in
water, but it does
not dissociate into
ions when it does
so.
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Electrolytes and Nonelectrolytes
Soluble ionic
compounds tend
to be
electrolytes.
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Electrolytes and Nonelectrolytes
Molecular
compounds tend to
be nonelectrolytes,
except for acids
and bases.
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Electrolytes
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A strong electrolyte
dissociates
completely when
dissolved in water.
A weak electrolyte
only dissociates
partially when
dissolved in water.
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Strong Electrolytes Are…
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Strong acids
Strong bases
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Strong Electrolytes Are…
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Strong acids
Strong bases
Soluble ionic salts
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Acids
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Arrhenius defined
acids as substances
that increase the
concentration of H+
when dissolved in
water.
Brønsted and Lowry
defined them as proton
donors.
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Acids
There are only seven
strong acids:
•
•
•
•
•
•
•
Hydrochloric (HCl)
Hydrobromic (HBr)
Hydroiodic (HI)
Nitric (HNO3)
Sulfuric (H2SO4)
Chloric (HClO3)
Perchloric (HClO4)
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Bases
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Arrhenius defined
bases as substances
that increase the
concentration of OH−
when dissolved in
water.
Brønsted and Lowry
defined them as
proton acceptors.
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Bases
The strong bases
are the soluble
metal salts of
hydroxide ion:
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•
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Alkali metals
Calcium
Strontium
Barium
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Types of solutions
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Acids- form H+ ions when dissolved.
Strong acids fall apart completely.
many ions
Memorize this list
H2SO4 HNO3 HCl HBr HI HClO3 HClO4
Weak acids- don’ dissociate completely.
Bases - form OH- ions when dissolved.
Strong bases- many ions.
KOH NaOH
Solubility
How much of a substance will
dissolve in a given amount of water.
 Usually g/100 mL
 Varies greatly, but if they do dissolve
the ions are separated,
 and they can move around.
 Water can also dissolve non-ionic
compounds if they have polar bonds.
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These things are soluble
1. Salts with alkali metals and
ammonium
2. Salts of nitrates and chlorates
3. Salts of sulfates except Ag+, Pb2+,
Hg22+, Ba2+,Ca2+ and Sr2+
4. Salts of chlorides, bromides &
iodides except Ag+, Pb2+, and Hg22+
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Solubility Rules
 Most hydroxides are slightly soluble
(insoluble) except NaOH and KOH
 Sulfides, carbonates, chromates, and
phosphates are insoluble
 Lower number rules supersede so
Na2S is soluble
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Is it soluble?
LiBr
 Ba(NO3)2
 CaSO4
 PbCl2
 CaCO3
 K2CO3
 Cd(ClO3)2
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Chemical Reactions
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All chemical reactions
have two parts
 Reactants - the substances you start
with
 Products- the substances you end up
with
 The reactants turn into the products.
 Reactants  Products
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In a chemical reaction
The way atoms are joined is changed
 Atoms aren’t created or destroyed.
 Can be described several ways
 In a sentence
– Copper reacts with chlorine to form
copper (II) chloride.
 In a word equation
 Copper + chlorine  copper (II) chloride
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Symbols used in equations
the arrow separates the reactants
from the products
 Read “reacts to form”
 Yields
 The plus sign = “and”
 (s) after the formula -solid
 (g) after the formula -gas
 (l) after the formula -liquid
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Symbols used in equations
(aq) after the formula - dissolved in
water, an aqueous solution.
 used after a product indicates a gas
(same as (g)) (products only)
 used after a product indicates a
solid (same as (s)) (products only)
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Symbols used in equations
indicates a reversible
reaction (More later)

heat
 
 ,    shows that heat
is supplied to the reaction
Pt
   is used to indicate a
catalyst used in this case, platinum.
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What is a catalyst?
A substance that speeds up a
reaction without being changed by
the reaction.
 A catalyst lowers the activation
energy
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Activation Energy- minimum amount of
energy required by reacting particles in
order to form the activated complex and
lead to a reaction
Skeleton Equation
Uses formulas and symbols to
describe a reaction
 doesn’t indicate how many.
 All chemical equations are sentences
that describe reactions.
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Convert these to equations
Solid iron (III) sulfide reacts with
gaseous hydrogen chloride to form
solid iron (II) chloride and hydrogen
sulfide gas.
 Nitric acid dissolved in water reacts
with solid sodium carbonate to form
liquid water and carbon dioxide gas
and sodium nitrate dissolved in
water.
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The other way
Fe(g) + O2(g)  Fe2O3(s)
 Cu(s) + AgNO3(aq) 
Ag(s) + Cu(NO3)2(aq)
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Balancing Chemical Equations
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Balanced Equation
Atoms can’t be created or destroyed
 All the atoms we start with we must
end up with
 A balanced equation has the same
number of atoms of each element on
both sides of the equation.
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C
+
O
O

O
C
O
C + O2  CO2
 This equation is already balanced
 What if it isn’t already?
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C
+
O
O

C
O
C + O2  CO
 We need one more oxygen in the
products.
 Can’t change the formula, because it
describes what actually happens
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C
+
O
O

C
O
Must be used to make another CO
 But where did the other C come
from?
 Must have started with two C
 2 C + O2  2 CO
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Rules for balancing
 Write the correct formulas for all the
reactants and products
 Count the number of atoms of each
type appearing on both sides
 Balance the elements one at a time
by adding coefficients (the numbers
in front)
 Check to make sure it is balanced.
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Never
Change a subscript to balance an
equation.
– If you change the formula you are
describing a different reaction.
– H2O is a different compound than
H2O2
 Never put a coefficient in the middle of
a formula
– 2 NaCl is okay, Na2Cl is not.
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Example
2 H2 + O2  H22H
O2O
R
P
4 2 H 2 4
2 O 1 2
The equation
Make
Changes
Also
Need
Recount
changes
twice
a table
theasOto
is
the
much
balanced,
keep
HH
Otrack
in the
has
of reactant
product
where
the same
you
number
are at of each kind of atom on both sides
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Example
2 H 2 + O2 
2 H 2O
R
P
4 2 H 2 4
2 O 1 2
This is the answer
Not this
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Examples
CH4 + O2  CO2 + H2O
AgNO3 + Cu  Cu(NO3)2 + Ag
Al + N2  Al2N3
P + O2  P4O10
Na + H2O  H2 + NaOH
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Techniques
If an atom appears more than once on
a side, balance it last.
 If you fix everything except one
element, and it is even on one side and
odd on the other, double the first
number, then move on from there.
 C4H10 + O2  CO2 + H2O
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Types of Reactions
Predicting the Products
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Types of Reactions
There are too many reactions to
remember
 Fall into categories.
 We will learn 5 types.
 Will be able to predict the products.
 For some we will be able to predict
whether they will happen at all.
 Must recognize them by the reactants
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#1 Combination Reactions
Combine - put together
 2 elements, or compounds combine
to make 1 compound.
 Ca +O2 CaO

SO3 + H2O  H2SO4
 We can predict the products if they
are two elements.
 Mg + N2 
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Write and balance
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Ca(s) + Cl2(g) 

Fe(s) + O2(g) 

Al(s) + O2(g) 
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Combining two compounds
If they tell you it is combination, you
will make one product
 Two compounds will make a
polyatomic ion.
 CO2 + H2O →
 H2O + Cl2O7→
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#2 Decomposition Reactions

decompose = fall apart

one reactant falls apart into two or
more elements or compounds.
electricity
NaCl   
 Na + Cl2

 CaCO3   CaO + CO2
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#2 Decomposition Reactions
Can predict the products if it is a
binary compound
 Made up of only two elements
 Falls apart into its elements
electricity

 H2O   
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#2 Decomposition Reactions
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
HgO  
#2 Decomposition Reactions
If the compound has more than two
elements you must be given one of
the products
 The other product will be from the
missing pieces
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 NiCO3   NiO +
 H2CO3(aq)CO2 +
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Single Replacement
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#3 Single Replacement
One element replaces another
 Reactants must be an element and a
compound.
 Products will be a different element
and a different compound.
 Na + KCl  K + NaCl
 F2 + LiCl  LiF + Cl2
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Na + KCl  K + NaCl
Na
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K
Cl
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F2 + 2 LiCl  2 LiF + Cl2
F
Li
Cl
Li
Cl
F
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#3 Single Replacement
Metals replace metals (and hydrogen)
 Al + CuSO4 
 Zn + H2SO4 
 Think of water as HOH
 Metals replace one of the H, combine
with hydroxide.
 Na + HOH 
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#3 Single Replacement
We can tell whether a reaction
will happen
 Some are more active than
other
 More active replaces less
active
 The complete list has been
given to you.
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#3 Single Replacement
Higher on the list replaces
lower.
 If the element by itself is
higher, it happens,
 if element by itself is lower, it
doesn’t
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#3 Single Replacement

Note the *
H can be replaced in acids
by everything higher
 Only the first 4 (Li - Na)
react with water.
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#3 Single Replacement
Al + HCl 
 Fe + CuSO4 
 Pb + KCl 
 Al + H2O 
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#3 Single Replacement
Nonmetals can replace other nonmetals
 Limited to F2 , Cl2 , Br2 , I2
 The order of activity is that on the table.
 Higher replaces lower.
 F2 + HCl 
 Br2 + KCl 
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Displacement Reactions
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
In displacement
reactions, ions oxidize an
element.
The ions, then, are
reduced.
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Displacement Reactions
In this reaction,
silver ions oxidize
copper metal.
Cu (s) + 2 Ag+ (aq)  Cu2+ (aq) + 2 Ag (s)
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Displacement Reactions
The reverse reaction,
however, does not
occur.
x Cu (s) + 2 Ag+ (aq)
Cu2+ (aq) + 2 Ag (s) 
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#4 Double Replacement
Two things replace each other.
 Reactants must be two ionic
compounds or acids.
 Usually in aqueous solution
 NaOH + FeCl3 
 The positive ions change place.
 NaOH + FeCl3 Fe3+OH- + Na+Cl NaOH + FeCl3 Fe(OH)3 + NaCl
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3NaOH + FeCl3 Fe(OH)3 + 3NaCl
Na+
O-
H+
Cl-
Na+
O-
H+
Cl-
Fe3+
Cl-
Na+
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O-
H+
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#4 Double Replacement
Will only happen if one of the
products
– doesn’t dissolve in water and
forms a solid
– or is a gas that bubbles out.
– or is a covalent compound usually
water.
 Polyatomic ions don’t change from
side to side
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Complete and balance
assume all of the reactions take
place.
 CaCl2(aq) + NaOH(aq) 
 CuCl2(aq) + K2S(aq) 
 KOH(aq) + Fe(NO3)3(aq) 
 H3PO4(aq) + Ca(OH)2(aq) 

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How to recognize which type
Look at the reactants
 E for element
 C for compound
E+E
Combination
C
Decomposition
 E + C Single replacement
 C + C Double replacement
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Types of Reactions
 Precipitation reactions
 When aqueous solutions of ionic
compounds are poured together a
solid forms.
 A solid that forms from mixed
solutions is a precipitate
 If you’re not a part of the solution,
your part of the precipitate
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Precipitation Reactions
When one mixes
ions that form
compounds that are
insoluble (as could
be predicted by the
solubility
guidelines), a
precipitate is
formed.
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Precipitation reaction
We can predict the products
 Can only be certain by experimenting
 The anion and cation switch partners
 AgNO3(aq) + KCl(aq) 
 Zn(NO3)2(aq) + BaCr2O7(aq) 
 CdCl2(aq) + Na2S(aq) 

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Precipitations Reactions
Only happen if one of the products is
insoluble
 Otherwise all the ions stay in
solution- nothing has happened.
 Need to use solubility rules to
determine if reaction takes place.
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Ionic Compounds and acids
Fall apart into ions when they dissolve
 That’s why they conduct electricity
when dissolved.
 So when we write them as (aq) they
are really separated
 NaCl(aq) is really Na+(aq) and Cl-(aq)
 K2SO4 (aq) is really K+(aq) and
SO42-(aq)
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Reactions in aqueous solutions
Many reactions happen in solution
 Makes it so the ions separate so they
can interact.
 Solids, liquids, and gases are not
separated, only aqueous
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Writing Net Ionic Equations
1.
2.
3.
4.
80
Write a balanced molecular
equation.
Dissociate all strong electrolytes.
Cross out anything that remains
unchanged from the left side to the
right side of the equation.
Write the net ionic equation with the
species that remain.
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Net ionic equations
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Written for single and double
replacement.
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Molecular Equation
The molecular equation lists the reactants
and products in their molecular form.
AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)
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82
Ionic Equation


In the ionic equation all strong electrolytes
(strong acids, strong bases, and soluble ionic
salts) are dissociated into their ions.
This more accurately reflects the species that
are found in the reaction mixture.
Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq) 
AgCl (s) + K+ (aq) + NO3- (aq)
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83
Net Ionic Equation



To form the net ionic equation, cross out anything that
does not change from the left side of the equation to the
right.
The only things left in the equation are those things that
change (i.e., react) during the course of the reaction.
Those things that didn’t change (and were deleted from
the net ionic equation) are called spectator ions.
Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) 
AgCl (s) + K+(aq) + NO3-(aq)
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Net Ionic Equation

To form the net ionic equation, cross out
anything that does not change from the left side
of the equation to the right.
Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) 
AgCl (s) + K+(aq) + NO3-(aq)
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85
Net Ionic Equation


To form the net ionic equation, cross out
anything that does not change from the left side
of the equation to the right.
The only things left in the equation are those
things that change (i.e., react) during the course
of the reaction.
Ag+(aq) + Cl-(aq)  AgCl (s)
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86
Write the Equation

MgSO4(aq) + NaOH(aq) →

H2SO4(aq) + KOH(aq) →

K3PO4(aq) + FeF3(aq) →
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Last Type
Combustion
 A compound composed of only C H
and maybe O is reacted with oxygen
 If the combustion is complete, the
products will be CO2 and H2O.
 If the combustion is incomplete, the
products will be CO and H2O.
 or just C and H2O.
 O2 will always be the second reactant

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Examples
Complete combustion of C4H10
 Incomplete combustion of C4H10
 Complete combustion of C6H12O6
 Incomplete combustion of C2H6O

90
Acid-Base Reactions
In an acid-base
reaction, the acid
donates a proton
(H+) to the base.
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Neutralization Reactions
Generally, when solutions of an acid and a base
are combined, the products are a salt and water.
CH3COOH (aq) + NaOH (aq) CH3COONa (aq) + H2O (l)
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Neutralization Reactions
When a strong acid reacts with a strong base, the
net ionic equation is…
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
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Neutralization Reactions
When a strong acid reacts with a strong base, the
net ionic equation is…
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq) 
Na+ (aq) + Cl- (aq) + H2O (l)
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Neutralization Reactions
When a strong acid reacts with a strong base, the
net ionic equation is…
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq) 
Na+ (aq) + Cl- (aq) + H2O (l)
H+ (aq) + OH- (aq)  H2O (l)
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Gas-Forming Reactions


Some metathesis reactions do not give the
product expected.
In this reaction, the expected product
(H2CO3) decomposes to give a gaseous
product (CO2).
CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l)
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Gas-Forming Reactions
When a carbonate or bicarbonate reacts
with an acid, the products are a salt,
carbon dioxide, and water.
CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l)
NaHCO3 (aq) + HBr (aq) NaBr (aq) + CO2 (g) + H2O (l)
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Gas-Forming Reactions
Similarly, when a sulfite reacts with an
acid, the products are a salt, sulfur
dioxide, and water.
SrSO3 (s) + 2 HI (aq) SrI2 (aq) + SO2 (g) + H2O (l)
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Gas-Forming Reactions
This reaction gives the predicted product,
but you had better carry it out in the hood,
or you will be very unpopular!
 But just as in the previous examples, a
gas is formed as a product of this
reaction.
Na2S (aq) + H2SO4 (aq)  Na2SO4 (aq) + H2S (g)

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Write the complete ionic equation
for

3+
-(aq)
+(aq)
-(aq) →
Fe
Br(aq)
K
OH
FeBr
(aq)
+
KOH(aq)
3
+(aq)
-(aq) + Fe(OH) (s)
K
Br
KBr
3
+
+
+
100
→
+
+
100
The complete ionic equation is
Fe3+(aq)+ Br-(aq) + K+(aq) +OH-(aq) →
K+(aq) +Br-(aq) + Fe(OH)3(s)
 K+ and Br- don’t change.
 They are spectator ions
 Could be eliminated
 Fe3+(aq) +OH-(aq) →Fe(OH)3(s)
 This is what really changes

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101
Net ionic equation
Shows only those particles that
change before and after.
 Eliminate spectator ions
 Needs to be balanced in terms of
both mass and charge
 Fe3+(aq) +OH-(aq) →Fe(OH)3(s)
 Fe3+(aq) +3 OH-(aq) →Fe(OH)3(s)

102
102
Write the net ionic equation
HCl (aq) + Ba(OH)2 (aq) →
 K2CO3(aq) + MgI2(aq) →
 CaCl2(aq) + MgSO4(aq) →
 Ba(OH)2(aq) + H2SO4(aq) →

103
103
Write the net ionic equation
Al(s) + FeSO4(aq) →
 Cl2(s) + NaI(aq) →

104
104
Predicting precipitates
Solids formed from aqueous solution.
 You can predict them if you know some
general rules for solubility.

105
105
Is there a reaction?
For double replacement- has to make
gas, solid or water.
 Water from an acid- H+ and a
hydroxide- OH- makes HOH
 Solids- from solubility rules
 Exchange ions and see if something
is insoluble

106
106