Chemical Reactions Occur
in Predictable Ways
Chapter 6
What You Will Learn
▪ Classifying reactions as one of six different types
1.
2.
3.
4.
5.
6.
Synthesis (Combination) Reactions
Decomposition Reactions
Single Replacement Reactions
Double Replacement Reactions
Neutralization (Acid-Base) Reactions
Combustion Reactions
What You Will Learn
▪ To predict the IDENTITY OF PRODUCTS of a chemical reaction
▪ To identify factors that affect the RATE of a chemical reaction
▪ To Define the RATE of a chemical reaction
▪ To explain role of CATALYSTS in a chemical reaction
Chapter 6 Assignment
▪ Assignment to be handed in as 1 package on test day:
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–
–
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Workbook complete
Check your understanding Page 271 *odds
Check your understanding Page 281 *odds
Chapter Review – Checking Concepts 1-4
Chapter 6 Project
▪ Making graphic organizers for 2 main concepts
▪ Page 282 – Prepare your own summary section *choose only 2
▪ Page 583 – Graphic organizers *must have 2 different types
– Venn diagram, Concept map, Spider Map, Flowchart, Cycle Chart etc… *choose 2
▪ Choose 2 of the following,
1. Six types of Chemical reactions
2. Classifying and predicting Products of Reactions Based on the Reactants
Only
3. Examples of Reactions Occurring at Different Rates
4. Four Factors Affecting the Rates of Reactions
6.1 Types of Chemical Reactions
DID YOU
KNOW??…
All known chemical reactions require
energy to break the chemical bonds in
the reactants.
Energy is often released when new
bonds form in the products.
LAB 6-1A Comparing Chemical Reactions
Purpose
• Read the Lab
• What is the purpose?
#4 Observation Table
• This is where you put your
observations!
What did you find out?
• #1-3 Full sentence responses
• Name & Date = Hand it in
▪ Lose marks for safety, clean up,
focus, professionalism, and
procedural issues.
▪ Full marks for being engaged,
safe, respectful, and a best
effort attempt.
▪ Due at end of class.
Steps to Writing Reactions
•
Some steps for doing reactions
1. Identify the type of reaction
2. Predict the product(s) using the type of reaction as
a model
3. Balance it
Don’t forget about the diatomic elements!
(BrINClHOF) For example, Oxygen is O2 as an
element.
1. Synthesis reactions
• Synthesis reactions occur when two substances (generally
elements) combine and form a compound. (Sometimes these are
called combination or addition reactions.)
reactant + reactant  1 product
• Basically: A + B  AB
• Example: 2H2 + O2  2H2O
• Example: C + O2  CO2
Synthesis Reactions
2K(g) + Cl2 (g)
2KCl (s)
Potassium + Chlorine
?
Practice
• Predict the products. Write and balance the following
synthesis 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
• Decomposition reactions occur when a compound breaks up
into the elements or into a few simpler compounds
• 1 Reactant  Product + Product
• In general: AB  A + B
• Example: 2 H2O  2H2 + O2
• Example: 2 HgO  2Hg + O2
Decomposition Reactions
2HgO(s)
What is
2Hg(l) + O2(g)
in this example?
Decomposition Exceptions FYI
• Carbonates and chlorates are special case decomposition
reactions that do not go to the elements.
• Carbonates (CO32-) decompose to carbon dioxide and a metal oxide
• Example: CaCO3  CO2 + CaO
• Chlorates (ClO3-) decompose to oxygen gas and a metal chloride
• Example: 2 Al(ClO3)3  2 AlCl3 + 9 O2
Practice
• Predict the products. Then, write and balance the following
decomposition reaction equations:
• Solid Lead (IV) oxide decomposes
PbO2(s) 
• Aluminum nitride decomposes
AlN(s) 
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) 
3. Single Replacement Reactions
• 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 element + compound
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
2Li(s) + 2H2O(l)
Lithium is a metal.
2LiOH(aq) + H2 (g)
Single Replacement Reactions
• Write and balance the following single replacement reaction
equation:
• Zinc metal reacts with aqueous hydrochloric acid
Zn(s) + HCl(aq)  ZnCl2 + H2(g)
2
Note: Zinc replaces the hydrogen
ion in the reaction
Single Replacement Reactions
• Sodium chloride solid reacts with fluorine gas
NaCl(s) + F2(g)  NaF(s) + Cl2(g)
Note that fluorine replaces chlorine in the compound
Is the equation balanced?
• Aluminum metal reacts with aqueous copper (II) nitrate
Al(s)+ Cu(NO3)2(aq)
4. Double Replacement Reactions
• Double Replacement Reactions occur when a metal replaces a
metal in a compound and a nonmetal replaces a nonmetal in a
compound
• Compound + compound  compound+ compound
• AB + CD  AD + CB
Double Replacement Reactions
• 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)  KNO3(aq) + BaSO4(s)
2
Practice
•
Predict the products. Balance the equation
1.
HCl(aq) + AgNO3(aq) 
2. CaCl2(aq) + Na3PO4(aq) 
3. Pb(NO3)2(aq) + BaCl2(aq) 
4. FeCl3(aq) + NaOH(aq) 
5. H2SO4(aq) + NaOH(aq) 
6. KOH(aq) + CuSO4(aq) 
Neutralization (Acid-Base) Reactions
▪ When an acid and base are mixed they will neutralize each other.
▪ An acid and base react to form a salt and water.
▪ Acid + Base
▪ HX + MOH
Salt + Water
MX + H2O
▪ X represents a negative ion -
▪ Practice problems on page 263
M represents a positive ion
5. Combustion Reactions
• 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
• In general:
CxHy + O2  CO2 + H2O
• Products in combustion are ALWAYS
carbon dioxide and water. (although
incomplete burning does cause some
by-products 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
•Example
• C5H12 + 8O2  5 CO2 + 6 H2O
•Write the products and balance the
following combustion reaction:
• C10H22 + O2 
Mixed Practice
•
State the type, predict the products, and balance the following
reactions:
1.
BaCl2 + H2SO4 
2.
C6H12 + O2 
3.
Zn + CuSO4 
4.
Cs + Br2 
5.
FeCO3 
6.2 Factors Affecting the Rate of
Chemical Reactions
1. Glow Sticks and Temperature
2. HCl and Concentration
3. Flour and Surface Area
4. Potassium Iodide and Catalysts
5. Diamonds and Pressure
Glow Sticks
A temperature demonstration
Single replacement reaction
between Mg and HCl
A concentration demonstration
Flour Special Effects
A surface area demonstration
Elephant Toothpaste!
A catalyst demonstration – adapted using yeast catalyst
How does the elephant toothpaste work?
▪ Foam is awesome! Each tiny foam bubble is filled with oxygen.
▪ The yeast acted as a catalyst to remove the oxygen from the hydrogen
peroxide. Since it did this very fast, it created lots and lots of bubbles.
▪ The bottle got warm. The experiment created a reaction called an
Exothermic Reaction - that means it not only created foam, it created
energy in the form of heat!
▪ The foam produced is just water, soap, and oxygen so you can clean it up
with a sponge and pour any extra liquid left in the bottle down the drain.
▪ This experiment is sometimes called "Elephant's Toothpaste" because it
looks like toothpaste coming out of a tube, but don't get the foam in your
mouth!
COLLISION MODEL
States that the rate of reaction is affected by the number of collisions
of reactant molecules.
Molecules in a gas or a liquid are constantly colliding with each other.
EXOTHERMIC:
Needs a little energy to get
started
Energy released overall
ENDOTHERMIC:
Lots of energy to get it
started
Energy absorbed overall
5 FACTORS
There are four factors that affect the rate of reaction that we
will discuss.
▪ TEMPERATURE
▪ CONCENTRATION
▪ SURFACE AREA
▪ CATALYSTS
▪ The 5th factor we will not discuss in this course. PRESSURE
TEMPERATURE
Higher temperatures increase the rate of a chemical
reaction because particles move faster at high
temperatures and this creates more violent
collisions more often.
Reaction Rate: Effect of Temperature
Activation Energy
• Arrhenius: molecules must posses a minimum
amount of energy to react.
• In order to form products, bonds must be broken
in the reactants.
– Bond breakage requires energy.
• Activation energy, Ea , is the minimum energy
required to initiate a chemical reaction.
Temperature and Rate
Activation Energy
Effect of temperature on rate
Increasing temperature increases the rate
Effect of temperature on rate
Conclusion
?
R
A
T
E
1
Rate increases
with increasing
temperature
Time
TEMPERATURE
CONCENTRATION
Higher concentration increase the rate of a chemical reaction
because there are more particles to collide with.
Effect of concentration on rate
Conclusion
?
R
A
T
E
1
Time
Rate is directly
proportional to
concentration
CONCENTRATION
SURFACE AREA
A larger surface area increases the rate of a chemical reaction
because there are more exposed particles in the
compound.
CATALYSTS
A substance that increases a chemical reaction but does not
get consumed by the reaction.
Therefore it is not considered a reactant or product.
Works by reducing the energy needed to break bonds,
provides easier paths for reactions. *lowers the Ae!
QUESTION
Explain how you would use your knowledge of factors that affect the
rate of reaction to cook a steak as quickly as possible.
▪ Temperature – increase to high
▪ Surface Area – Cut steak into pieces (increase area)
▪ Concentration – none
▪ Cataylsts - none
QUESTION
What effect on the rate of reaction of a metal with 20 ml of
dilute acid at room temperature would you expect if:
A) the acid was cooled to 100C?
B) 2 ml of concentrated acid was added?
C) the metal was ground into powder before addition to
the acid?
ANSWER
A) The reaction rate would decrease (slow down)
B) the reaction rate would increase
( speed up)
C) the reaction rate would increase
( speed up )
MENTOS GEYSER
Let’s go outside!
Iodine Clock
Probably the best rate of reaction demonstration ever!
Iodine clock explained
▪ It is called a clock reaction because you can change the amount if
time it takes for the liquids to turn blue.
▪ The chemistry of the demonstration gets a bit complicated, but
basically it is a battle of chemistry between the starch which is trying
to turn the iodine blue, and the Vitamin C which is keeping it from
turning blue. Eventually the Vitamin C loses and, bam! - you get
instant blueness.
Iodine Clock *different reactants but
essentially the same– Thanks Wikipedia!
▪ This reaction starts from a solution of hydrogen peroxide with sulfuric acid. To this is added a solution
containing potassium iodide, sodium thiosulfate, and starch. There are two reactions occurring in the
solution.
▪ In the first, slow reaction, iodine is produced:
▪ H2O2 + 2I- + 2H+ → I2 + 2H2O
▪ In the second, fast reaction, iodine is reconverted to 2 iodide ions by the thiosulfate:
▪ 2S2O32- + I2 → S4O62- + 2I▪ After some time the solution always changes colour to a very dark blue, almost black.
▪ When the solutions are mixed, the second reaction causes the triiodide ion to be consumed much faster than
it is generated, and only a small amount of triiodide is present in the dynamic equilibrium. Once the
thiosulfate ion has been exhausted, this reaction stops and the blue colour caused by the triiodide – starch
complex appears.
▪ Anything that accelerates the first reaction will shorten the time until the solution changes color. Decreasing
the pH (increasing H+ concentration), or increasing the concentration of iodide or hydrogen peroxide will
shorten the time. Adding more thiosulfate will have the opposite effect; it will take longer for the blue colour
to appear.