Transcript Chemical Reactions - Seward County Community College

Chemical Reactions
Physical Science Chapter 13
Types of Reactions
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There are four types of chemical
reactions we will talk about:
1.
2.
3.
4.
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Combination reactions
_____________ reactions
Single replacement reactions
________________ reactions
You need to be able to identify the type
of reaction and predict the product(s)
Steps to Writing Reactions
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Some steps for doing reactions
1.
2.
3.
Identify the type of reaction
Predict the product(s) using the type of
reaction as a model
Balance it
Don’t forget about the diatomic elements!
(BrINClHOF) For example, Oxygen is O2 as an
element.
In a compound, it can’t be a diatomic element
because it’s not an element anymore, it’s a
compound!
1. Combination reactions
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Combination reactions occur when two
substances (generally elements) combine
and form a compound. (Sometimes these are
called synthesis or addition reactions.)
reactant + reactant  1 product
Basically: A + B  AB
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Example: 2H2 + O2  2H2O
Example: C + O2  CO2
Combination Reactions
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Here is another example of a combination
reaction
Practice
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Predict the products. Write and balance
the following combination reaction
equations.
Sodium metal reacts with chlorine gas
Na(s) + Cl2(g) 
Solid Magnesium reacts with fluorine gas
Mg(s) + F2(g) 
Aluminum metal reacts with fluorine gas
Al(s) + F2(g) 
2. Decomposition Reactions
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Decomposition reactions occur when a
compound breaks up into the elements or
in a few to simpler compounds
1 Reactant  Product + Product
In general: AB  A + B
Example: 2 H2O  2H2 + O2
Example: 2 HgO  2Hg + O2
Decomposition Reactions
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Another view of a decomposition reaction:
Decomposition Exceptions
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Carbonates and chlorates are special case
decomposition reactions that do not go to
the elements.
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Carbonates (CO32-) decompose to carbon
dioxide and a metal oxide
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Chlorates (ClO3-) decompose to oxygen gas
and a metal chloride
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Example: CaCO3  CO2 + CaO
Example: 2 Al(ClO3)3  2 AlCl3 + 9 O2
There are other special cases, but we will not
explore those in Chemistry I
Practice
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Predict the products. Then, write and
balance the following decomposition
reaction equations:
Solid Lead (IV) oxide decomposes
PbO2(s) 
Aluminum nitride decomposes
AlN(s) 
Chemical Reaction Review
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In each of the following animations
determine if a chemical reaction did occur
On what evidence did you base your
decision
Animation Link
Chemical Reaction Review
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1.
2.
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Identify the type of reaction and whether it is
exothermic or endothermic
Reaction #1
Reaction #2
Write the balanced decomposition reaction for water.
Is there more, less, or the same amount of hydrogen
gas produced when compared to oxygen? Based on
the chemical equation what is the ratio of hydrogen to
oxygen gas produced?
Animation check of prediction
Chemistry in Auto Safety
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Airbag Deployment Video
Airbag Chemistry
Practice
Identify the type of reaction for each of the
following synthesis or decomposition
reactions, and write the balanced equation:
N2(g) + O2(g)  Nitrogen monoxide
BaCO3(s) 
Co(s)+ S(s)  (make Co be +3)
NH3(g) + H2CO3(aq) 
NI3(s) 
Energy and Rate of Reaction
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Arrhenius believed that for molecules to react
upon collision, they must become "activated,"
known as the Activation Energy.
Heat Flow During a Reaction
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Exothermic
Combustion of gasoline
 Cellular Respiration
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Endothermic
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Example: Photosynthesis
Factors Influencing Reaction Rates
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Increase surface area of reactants
Increase temperature
Increase reactant concentration
Addition of a catalyst
Catalysts
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It is not always practical or convenient to
increase reaction rates by increasing the
temperature or other reaction factors
A Catalyst is a substance that speeds up a
reaction without being consumed during
by the reaction
Catalysts are used to speed up reactions
without changing the temperature
Catalysts at Work
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Catalysts are used in a huge variety
of ways because they can enhance
reaction rates by many orders of
magnitude!
In general, they work by lowering
the activation energy to a reaction.
Catalysts at Work
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1.
2.
Activity:
Draw an activation energy graph for a
chemical reaction
Draw an activation energy curve on the
graph that would represent the impact of
using a catalyst
Impact of a Catalyst
Catalyst Example
2N2O(g)  2N2(g) + O2(g)
Catalyst Example - Enzymes
The Chemistry of
Acids and Bases
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Physical Science
Chapter 13
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Acid and Bases
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Acid and Bases
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Acid and Bases
Acids
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Have a sour taste. Vinegar is a solution of acetic acid. Citrus
fruits contain citric acid.
React with certain metals to produce hydrogen gas.
React with carbonates and bicarbonates to produce carbon
dioxide gas
Bases
Have a bitter taste.
Feel slippery. Many soaps contain bases.
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Some Properties of Acids
Produce H+ (as H3O+) ions in water (the hydronium ion is a
hydrogen ion attached to a water molecule)
Taste sour
Corrode metals
Electrolytes
React with bases to form a salt and water
pH is less than 7
Turns blue litmus paper to red “Blue to Red A-CID”
Acid Nomenclature Review
Anion
Ending
Binary 
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Acid Name
-ide
hydro-(stem)-ic acid
-ate
(stem)-ic acid
-ite
(stem)-ous acid
Ternary
An easy way to remember which goes with which…
“In the cafeteria, you ATE something ICky”
Acid Nomenclature Flowchart
ACIDS
start with 'H'
2 elements
3 elements
hydro- prefix
-ic ending
no hydro- prefix
-ate ending
becomes
-ic ending
-ite ending
becomes
-ous ending
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Acid Nomenclature Review
• HBr (aq)
hydrobromic acid
• H2CO3
carbonic acid
• H2SO3
sulfurous acid
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Name ‘Em!
• HI (aq)
• HCl (aq)
• H2SO3
• HNO3
• HIO4
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Some Properties of Bases
 Produce OH- ions in water
 Taste bitter, chalky
 Are electrolytes
 Feel soapy, slippery
 React with acids to form salts and water
 pH greater than 7
 Turns red litmus paper to blue
“Basic Blue”
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Some Common Bases
NaOH
sodium hydroxide
KOH potassium hydroxide
lye
liquid soap
Ba(OH)2
barium hydroxide
stabilizer for plastics
Mg(OH)2
magnesium hydroxide “MOM” Milk of magnesia
Al(OH)3
aluminum hydroxide
Maalox (antacid)
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Acid/Base definitions
• Definition #1: Arrhenius (traditional)
Acids – produce H+ ions (or hydronium ions
H3O+)
Bases – produce OH- ions
(problem: some bases don’t have hydroxide
ions!)
Arrhenius acid is a substance that produces
H+ (H3O+)
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in water
Arrhenius base is a substance that produces OH- in water
The pH scale is a way of
expressing the strength
of acids and bases.
Instead of using very
small numbers, we just
use the NEGATIVE
power of 10 on the
Molarity of the H+ (or
OH-) ion.
Under 7 = acid
7 = neutral
Over 7 = base
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pH of Common Substances
Calculating the pH
pH = - log [H+]
(Remember that the [ ] mean Molarity)
Example: If [H+] = 1 X 10-10
pH = - log 1 X 10-10
pH = - (- 10)
pH = 10
Example: If [H+] = 1.8 X 10-5
pH = - log 1.8 X 10-5
pH = - (- 4.74)
pH = 4.74
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Try These!
Find the pH of these:
1) A 0.15 M solution of
Hydrochloric acid
2) A 3.00 X 10-7 M solution
of Nitric acid
pH testing
• There are several ways to test pH
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Blue litmus paper (red = acid)
Red litmus paper (blue = basic)
pH paper (multi-colored)
pH meter (7 is neutral, <7 acid, >7 base)
Universal indicator (multi-colored)
Indicators like phenolphthalein
Natural indicators like red cabbage, radishes
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Paper testing
• Paper tests like litmus paper and pH
paper
– Put a stirring rod into the solution and stir.
– Take the stirring rod out, and place a drop of the
solution from the end of the stirring rod onto a
piece of the paper
– Read and record the color change. Note what the
color indicates.
– You should only use a small portion of the paper.
You can use one piece of paper for several tests.
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pH meter
• Tests the voltage of the
electrolyte
• Converts the voltage to
pH
• Very cheap, accurate
• Must be calibrated with
a buffer solution
pH indicators
• Indicators are dyes that can be
added that will change color in
the presence of an acid or base.
• Some indicators only work in a
specific range of pH
• Once the drops are added, the
sample is ruined
• Some dyes are natural, like radish
skin or red cabbage
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3. Single Replacement Reactions
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Single Replacement Reactions occur when
one element replaces another in a compound.
A metal can replace a metal (+) OR
a nonmetal can replace a nonmetal (-).
element + compound product + product
A + BC  AC + B (if A is a metal) OR
A + BC  BA + C (if A is a nonmetal)
(remember the cation always goes first!)
When H2O splits into ions, it splits into
H+ and OH- (not H+ and O-2 !!)
Single Replacement Reactions
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Another view:
Single Replacement Reactions
Write and balance the following single
replacement reaction equation:
• Zinc metal reacts with aqueous
hydrochloric acid
Zn(s) + 2 HCl(aq)  ZnCl2 + H2(g)
Note: Zinc replaces the hydrogen ion in the
reaction
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Single Replacement Reactions
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Sodium chloride solid reacts with fluorine gas
2 NaCl(s) + F2(g)  2 NaF(s) + Cl2(g)
Note that fluorine replaces chlorine in the compound
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Aluminum metal reacts with aqueous copper
(II) nitrate
Al(s)+ Cu(NO3)2(aq)
4. Double Replacement Reactions
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Double Replacement Reactions occur
when a metal replaces a metal in a compound
and a nonmetal replaces a nonmetal in a
compound
Compound + compound  product +
product
AB + CD  AD + CB
Double Replacement Reactions
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Think about it like “foil”ing in algebra, first and
last ions go together + inside ions go together
Example:
AgNO3(aq) + NaCl(s)  AgCl(s) + NaNO3(aq)
Another example:
K2SO4(aq) + Ba(NO3)2(aq)  2 KNO3(aq) + BaSO4(s)
Practice
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Predict the products. Balance the equation
5.
HCl(aq) + AgNO3(aq) 
CaCl2(aq) + Na3PO4(aq) 
Pb(NO3)2(aq) + BaCl2(aq) 
FeCl3(aq) + NaOH(aq) 
H2SO4(aq) + NaOH(aq) 
6.
KOH(aq) + CuSO4(aq) 
1.
2.
3.
4.
5. Combustion Reactions
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Combustion reactions
occur when a hydrocarbon
reacts with oxygen gas.
This is also called
burning!!! In order to burn
something you need the 3
things in the “fire
triangle”:
1) A Fuel (hydrocarbon)
2) Oxygen to burn it with
3) Something to ignite the
reaction (spark)
Combustion Reactions
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In general:
CxHy + O2  CO2 + H2O
Products in combustion are
ALWAYS carbon dioxide and
water. (although incomplete
burning does cause some byproducts like carbon monoxide)
Combustion is used to heat
homes and run automobiles
(octane, as in gasoline, is C8H18)
Combustion
Reactions
Edgar Allen Poe’s
drooping eyes and
mouth are potential
signs of CO
poisoning.
Combustion
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Example
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C5H12 + 8 O2  5 CO2 + 6 H2O
Write the products and balance the
following combustion reaction:
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C10H22 + O2 
Mixed Practice
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1.
2.
3.
4.
5.
State the type, predict the products, and
balance the following reactions:
BaCl2 + H2SO4 
C6H12 + O2 
Zn + CuSO4 
Cs + Br2 
FeCO3 
Weblinks
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Chemical Reaction Video Clips