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I II III IV V C. Johannesson
I. Intro to Reactions
(p. 241 – 250)
Ch. 8 – Chemical Reactions
APPETIZER
Below is a chemical equation
representing the decomposition
reaction of ammonium dichromate
into nitrogen chromium (III) oxide,
and water.
(NH4)2Cr2O7(s) ----> N2(g) + Cr2O3(s) + 4H2O(g)
C. Johannesson
APPETIZER
KEY idea: In a chemical reaction,
new compounds are formed by bonds
being broken, atoms rearranging, and
new bonds forming.
(NH4)2Cr2O7(s) ----> N2(g) + Cr2O3(s) + 4H2O(g)
C. Johannesson
APPETIZER
Can you think of any chemical
reactions that you come in contact
with on a daily basis?
Pharaoh’s Serpent
C. Johannesson
C. Johannesson
A.Signs of a Chemical Reaction
Evolution of heat and light
Formation of a gas
Color change
Formation of a precipitate
C. Johannesson
B.Law of Conservation of Mass
mass is neither created nor destroyed
in a chemical reaction
4 H
2 O
4 H
2 O
4 g 32 g
36 g
total mass stays the same
atoms can only rearrange
C. Johannesson
C. Chemical Equations
A+B C+D REACTANTS PRODUCTS
C. Johannesson
D. Writing Equations
Identify the substances involved.
Use symbols to show:
2H2(g) + O2(g) 2H2O(g)
How many? - coefficient
Of what? - chemical formula
In what state? - physical state
Remember the diatomic elements.
C. Johannesson
p. 246
C. Chemical Equations
D. Writing Equations
Two atoms of aluminum react with
three units of aqueous copper(II)
chloride to produce three atoms of
copper and two units of aqueous
aluminum chloride.
• How many?
• Of what?
• In what state?
Al 2 (s) + 3 CuCl2 (aq) 3 Cu (s) + 2 AlCl3 (aq)
E. Describing Equations
Describing Coefficients:
individual atom = “atom”
covalent substance = “molecule”
ionic substance = “unit”
3 molecules of carbon dioxide
2 atoms of magnesium
4 units of magnesium oxide
3CO2
2Mg
4MgO
E. Describing Equations
to produce
• How many?
• Of what?
• In what state?
Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)
One atom of solid zinc reacts with
two molecules of aqueous hydrogen
chloride (hydrochloric acid)
one unit of aqueous zinc chloride
and one molecule of hydrogen gas.
I II III IV V C. Johannesson
II. Balancing Equations
(p. 250-254)
Ch. 8 – Chemical Reactions
Appetizer:
What is “wrong” with these two
pictures?
C. Johannesson
C. Johannesson
A. Balancing Steps
1. Write the unbalanced equation.
2. Count atoms on each side.
3. Add coefficients to make #s equal.
Coefficient subscript = # of atoms
4. Reduce coefficients to lowest
possible ratio, if necessary.
5. Double check atom balance!!!
C. Johannesson
B. Helpful Tips
Balance one element at a time.
Update ALL atom counts after adding
a coefficient.
If an element appears more than
once per side, balance it last.
Balance polyatomic ions as single
units.
“1 SO4” instead of “1 S” and “4 O”
C. Johannesson
Al + CuCl2 Cu + AlCl3
Al
Cu
Cl
1 1
1 1
2 3
2
3
6
3
3 3 2
C. Balancing Example
Aluminum and copper(II) chloride react
to form copper and aluminum chloride.
2
2
6
E2
___C8H18 + ___ O2 ___CO2 + ___H2O
C. Johannesson
E3
Aluminum sulfate solution and
calcium hydroxide solution produce a
precipitate of aluminum hydroxide
and solid calcium sulfate.
C. Johannesson
E4
___FeS + ___ O2 ___Fe2O3 + ___SO2
C. Johannesson
I II III IV V C. Johannesson
Ch. 8 – Chemical Reactions
III. Types of
Chemical
Reactions (p. 256 - 267)
C. Johannesson
A. Combustion
CH4(g) + 2O2(g) CO2(g) + 2H2O(g)
the burning of any substance in O2 to
produce heat
A + O2 B
C. Johannesson
Na(s)+ O2(g)
C3H8(g)+ O2(g) 5 3 4
A. Combustion
Products:
contain oxygen
hydrocarbons form CO2 + H2O
CO2(g)+ H2O(g)
Na2O(s) 4 2
C. Johannesson
B. Synthesis
the combination of 2 or more
substances to form a compound
only one product
A + B AB
Synthesis Reaction
C. Johannesson
+
C. Johannesson
B. Synthesis
H2(g) + Cl2(g) 2 HCl(g)
C. Johannesson
Al(s)+ Cl2(g) AlCl3(s) 2 3 2
B. Synthesis
Products:
ionic - cancel charges
covalent - hard to tell
C. Johannesson
C. Decomposition
a compound breaks down into 2 or
more simpler substances
only one reactant
AB A + B
Decompostion Reaction
C. Johannesson
+
C. Johannesson
C. Decomposition
2 H2O(l) 2 H2(g) + O2(g)
C. Johannesson
KBr(l) K(s) + Br2(l) 2 2
C. Decomposition
Products:
binary - break into elements
others - hard to tell
32
The “Activity Series” of Metals Lithium
Potassium
Calcium
Sodium
Magnesium
Aluminum
Zinc
Chromium
Iron
Nickel
Lead
Hydrogen
Bismuth
Copper
Mercury
Silver
Platinum
Gold
1) Metals can replace other
metals, provided they are
above the metal they are
trying to replace (for example, zinc will replace lead)
2) Metals above hydrogen can
replace hydrogen in acids.
3) Metals from sodium upward
can replace hydrogen in
water.
Higher
activity
Lower
activity
33
The “Activity Series” of Halogens
Fluorine
Chlorine
Bromine
Iodine
Halogens can replace other
halogens in compounds,
provided they are above the
halogen they are trying to
replace.
2NaCl(s) + F2(g) 2NaF(s) + Cl2(g)
MgCl2(s) + Br2(g) ??? No Reaction!
???
Higher Activity
Lower Activity
C. Johannesson
D. Single Displacement
one element replaces another in a
compound
metal replaces metal (+)
nonmetal replaces nonmetal (-)
A + BC B + AC
C. Johannesson
D. Single displacement
Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s)
C. Johannesson
Fe(s)+ CuSO4(aq) Cu(s)+ FeSO4(aq)
D. Single Replacement
Products:
metal metal (+)
nonmetal nonmetal (-)
free element must be more active
(check activity series)
Br2(l)+ NaCl(aq) N.R.
C. Johannesson
AB + CD AD + CB
E. Double Displacement
ions in two compounds “change
partners”
cation of one compound combines
with anion of the other
C. Johannesson
E. Double Displacement
Pb(NO3)2(aq) + K2CrO4(aq) PbCrO4(s) + 2KNO3(aq)
C. Johannesson
Pb(NO3)2(aq)+ KI(aq) PbI2(s)+ KNO3(aq)
E. Double Displacement
Products:
switch negative ions
one product must be insoluble
(check solubility table)
NaNO3(aq)+ KI(aq) N.R.
2 2
I II III IV V C. Johannesson
IV. Reaction Energy
(p. 514 - 517)
Ch. 17 – Chemical Reactions
C. Johannesson
A. Reaction Pathway
Shows the change in energy during a
chemical reaction
C. Johannesson
B. Exothermic Reaction
reaction that
releases
energy
products have
lower PE
than reactants
2H2(l) + O2(l) 2H2O(g) + energy
energy
released
C. Johannesson
C. Endothermic Reaction
reaction that
absorbs
energy
reactants have
lower PE
than products
2Al2O3 + energy 4Al + 3O2
energy
absorbed
I II III IV V C. Johannesson
V. Reaction Rate
(p. 532 - 541)
Ch. 17 – Chemical Reactions
C. Johannesson
A. Collision Theory
Reaction rate depends on the
collisions between reacting particles.
Successful collisions occur if the
particles...
collide with each other
have the correct orientation
have enough kinetic energy to
break bonds
C. Johannesson
A. Collision Theory
Particle Orientation
Required Orientation
Successful Collision
Unsuccessful
Collisions
C. Johannesson
A. Collision Theory
Activation Energy (Ea)
minimum energy required for a
reaction to occur
Activation
Energy
C. Johannesson
A. Collision Theory
Activation Energy
depends on reactants
low Ea = fast rxn rate
Ea
C. Johannesson
B. Factors Affecting Rxn Rate
Surface Area
high SA = fast rxn rate
more opportunities for collisions
Increase surface area by…
-using smaller particles
-dissolving in water
C. Johannesson
B. Factors Affecting Rxn Rate
Concentration
high conc = fast rxn rate
more opportunities for collisions
C. Johannesson
B. Factors Affecting Rxn Rate
Temperature
high temp = fast rxn rate
high KE
- fast-moving particles
-more likely to reach activation
energy
C. Johannesson
B. Factors Affecting Rxn Rate
Temperature
Analogy: 2-car collision
5 mph “fender bender”
50 mph “high-speed crash”
C. Johannesson
B. Factors Affecting Rxn Rate
Catalyst
substance that increases rxn rate
without being consumed in the rxn
lowers the activation energy
C. Johannesson
B. Factors Affecting Rxn Rate
Enzyme Catalysis
