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3 Factors Affecting the Rates of Chemical Reactions Next Slide When
Chemists study reactions, they have observed many factors that
increase or decrease the over all concentration per unit time.
These changes have allowed for advancements in chemical research,
specifically in Chemical Kinetics. Slide 4 Factors Affecting the
Rate of Chemical Reactions Next Slide By definition, CHEMICAL
KINETICS is the study of chemical reactions, specifically looking
at the quantitative (numerical/mathematical) study of reaction
rates. A REACTION RATE (sometimes referred to as the speed of a
reaction) is the change of concentration of reactants or products
per unit time. In other words, it is how fast or slow a reaction
takes place. It is important to understand that reaction rates
allow chemists to differ between slow reactions, like the oxidation
of iron into rust, and fast reactions, like the combustion of fire
works. Slide 5 Factors Affecting the Rate of Chemical Reactions
Next Slide Slide 6 Factors Affecting the Rate of Chemical Reactions
Next Slide The Second Factor which affects the Rate of Chemical
Reactions is the CONCENTRATION of the REACTANTS during a reaction.
HIGHER CONCENTRATION, implies that more molecules will be available
for interaction with other molecules, thus increasing the rate.
LOWER CONCENTRATION, implies that less molecules will interact with
each other, thus decreasing the rate. In the video, you see a
difference in the concentration of coal particles. Obviously, on
the left, there arent as many particles compared to the right. Thus
it is right to say that the flame on the right is burning more coal
than the flame on the left. Thus the rate of the flame on the right
is greater because more coal is being burned for the same unit
time. Slide 7 Factors Affecting the Rate of Chemical Reactions Next
Slide The Third Factor which affects the Rate of Chemical Reactions
is the TEMPERATURE in which the reaction takes place. HIGHER
TEMPERATURE, implies that molecules will be moving quicker and will
interact more often, increasing the likeability that the molecules
will interact properly, speeding up the rate of reaction. LOWER
TEMPERATURE, implies that molecules will be moving slower,
decreasing the likeability that molecules will interact properly,
slowing down the rate of reaction. Slide 8 Factors Affecting the
Rate of Chemical Reactions Next Slide The Fourth Factor which
effects the Rate of Chemical Reactions is CATALYSTS. A catalyst is
meant to speed up a reaction while decreasing the activation energy
of a reaction. It is important to note that a catalyst in a
reaction will be produced in the reaction, otherwise it is not a
catalyst! In biology, ENZYMES are the catalyst of frequent topic
because it allows our body to undergo reaction with minimal energy
requirements in a efficient manner. In the video you see the
dissociation of hydrogen peroxide into water and oxygen with the
help of the catalyst manganese dioxide which remains constant in
system. The presence of the catalyst increases the rate of reaction
which normally would be extremely slow. Slide 9 Factors Affecting
the Rate of Chemical Reactions Next Slide The Fifth and Final
Factor which effects the Rate of Reaction is the PHYSICAL STATE OF
THE REACTANTS. The physical state of reactants can largely effect
the rate of a reaction because it effects whether or not a
sufficient amount of reactants can react. Suppose you are trying to
burn a log of wood, the combustion of the organic compound will
only react on the surface, because the center of the log isnt it
contact with oxygen and fire which is required for this reaction.
Thus, the SURFACE AREA of reactants will effect the rate of
reaction. Also, a compound in AQUEOUS form allows for movement of
the compound in a reaction. Thus, if reactants are dissolved in
solution, the rate of reaction will increase. Slide 10 Answer
QUESTION 1 Chemical Kinetics is the __________ study of reaction
_________. a)Qualitative, Rates b)Quantitative, Rates
c)Qualitative, Processes d)Quantitative, Processes Factors
Affecting the Rate of Chemical Reactions Slide 11 Next Question
QUESTION 1 ANSWER Chemical Kinetics is the QUANTITATIVE study of
reaction RATES. a)Qualitative, Rates b)Quantitative, Rates
c)Qualitative, Processes d)Quantitative, Processes Factors
Affecting the Rate of Chemical Reactions Next Section Slide 12
Answer QUESTION 2 (Pulled from winter midterm 2011) Which of the
following statements is false? A. The rate of a reaction usually
increases when the concentration of one of the reactants is
increased. B. The rate of a reaction is dependent on temperature.
C. The rate of a reaction may be increased by certain catalytic
agents. D. A reaction will proceed rapidly if the activation energy
is large. E. The rate of a reaction describes the change in
concentration of a reactant or product with time. Factors Affecting
the Rate of Chemical Reactions Slide 13 Next Question Factors
Affecting the Rate of Chemical Reactions Next Section QUESTION 2
ANSWER Which of the following statements is false? A. The rate of a
reaction usually increases when the concentration of one of the
reactants is increased. B. The rate of a reaction is dependent on
temperature. C. The rate of a reaction may be increased by certain
catalytic agents. D. A reaction will proceed rapidly if the
activation energy is large. E. The rate of a reaction describes the
change in concentration of a reactant or product with time. Slide
14 Answer QUESTION 3 Which one of the following reactions reacts
the most rapidly at room temperature. A) 2 H 2 + O 2 2 H 2 O B) H +
+ OH - H 2 O (neutralization) C) C 12 H 22 O 11 (sugar) 12 C + 11 H
2 O D) 4Fe + 3O 2 2Fe 2 O 3 Factors Affecting the Rate of Chemical
Reactions Slide 15 Next Question Factors Affecting the Rate of
Chemical Reactions Next Section QUESTION 3 ANSWER Which one of the
following reactions reacts the most rapidly at room temperature. A)
2 H 2 + O 2 2 H 2 O B) H + + OH - H 2 O (neutralization) C) C 12 H
22 O 11 (sugar) 12 C + 11 H 2 O D) 4Fe + 3O 2 2Fe 2 O 3 *** IONS
REACT THE QUICKEST! Slide 16 Answer QUESTION 4 (pulled from the
University of Waterloo Chemical Kinetics website) Which one of the
following burns easily and why? A) a bar of steel B) steel sheet C)
steel wool D) steel pipe Factors Affecting the Rate of Chemical
Reactions Slide 17 Next Question Factors Affecting the Rate of
Chemical Reactions Next Section QUESTION 4 ANSWER Which one of the
following burns easily and why? A) a bar of steel B) steel sheet C)
steel wool D) steel pipe *** Surface Area is greatly increased and
allows for the steel to burn. Slide 18 Answer QUESTION 5
Glycolysis, an energy pathway in both anaerobic and aerobic bodies,
is undergone in organisms. What is the greatest factor that allows
this reaction to occur? A) Catalyst B) Temperature C) Nature of
Reactants D) Physical State of Reactants E) Reactant Concentration
Factors Affecting the Rate of Chemical Reactions Slide 19 Next
Section QUESTION 5 ANSWER Glycolysis, an energy pathway in both
anaerobic and aerobic bodies, is the process of breaking done
Glucose into products in organisms. What is the most likely factor
that allows this reaction to occur? A) Catalyst B) Temperature C)
Nature of Reactants D) Physical State of Reactants E) Reactant
Concentration The activation energy of glucose is decreased in
every intermediate step and allows for minimal amounts of energy to
be used by organisms to break the molecule because organisms do not
have the capabilities to combust this sugar. Slide 20 Average and
Instantaneous Rates of Change Next Slide Because the rate of
reaction is defined as being the change in concentration over the
change in time, it is proper practice to discuss average and
instantaneous rates of change. Slide 21 Average and Instantaneous
Rates of Change Next Slide An AVERAGE RATE of change is quantified
by the following equation: This equation allows us to determine the
Average Rate when given information in a chart and if given
information in a graph. Graphically, the average rate of change is
the slope of a line between two points often referred to as the
secant. t (in s) [A] Slide 22 Average and Instantaneous Rates of
Change Next Slide An INSTANTANEOUS RATE of change is quantified by
the following equation: This equation allows us to determine the
Instantaneous Rate when given a single concentration at a moment of
time. Graphically, the instantaneous rate of change is the tangent
of a point. t (in s) [A] Slide 23 Average and Instantaneous Rates
of Change Next Slide Because the Rate of Reaction can be determined
for any reactant or product in a reaction, there must be a way to
differ between Reactants and Products. We will define the RATE OF
CONSUMPTION to be the rate of which the reactants are used. We will
define the RATE OF PRODUCTION to be the rate of which the products
are used. Slide 24 Answer QUESTION 6 What is the Average Rate of
Change for the following equation given the following chart of
data? a.Between 10 and 0 for oxygen gas b.Between 20 and 30 for
Glucose (sugar) Average and Instantaneous Rates of Change Slide 25
Next Question QUESTION 6 ANSWER What is the Average Rate of Change
for the following equation given the following chart of data?
a.Between 10 and 0 for oxygen gas b.Between 20 and 30 for Glucose
(sugar) Average and Instantaneous Rates of Change Next Section
Slide 26 Answer QUESTION 8 What is the Rate of Production of Carbon
dioxide given the following data? a)From 0 seconds to 10 seconds
b)From 20 seconds to 30 seconds Average and Instantaneous Rates of
Change Slide 27 Next Question QUESTION 8 ANSWER What is the Rate of
Production of Carbon dioxide given the following data? a)From 0
seconds to 10 seconds b)From 20 seconds to 30 seconds Average and
Instantaneous Rates of Change Next Section Slide 28 Answer QUESTION
9 (Pulled from winter midterm 2011) Sucrose is fermented to ethanol
and carbon dioxide in the following reaction. C 12 H 22 O 11(aq) +
H 2 O (l) 4 CH 3 CH 2 OH (aq) + 4 CO 2(g) If the rate of production
of CO 2 is 0.250 mol/Ls, then what is the rate of consumption of C
12 H 22 O 11 ? A)1.00 mol/Ls B) 6.25102 mol/Ls C) 0.250 mol/Ls D)
4.00 mol/Ls E) 0.125 mol/Ls Average and Instantaneous Rates of
Change Slide 29 Next Section QUESTION 9 ANSWER Sucrose is fermented
to ethanol and carbon dioxide in the following reaction. C 12 H 22
O 11(aq) + H 2 O (l) 4 CH 3 CH 2 OH (aq) + 4 CO 2(g) If the rate of
production of CO 2 is 0.250 mol/Ls, then what is the rate of
consumption of C 12 H 22 O 11 ? A)1.00 mol/Ls B) 6.25102 mol/Ls C)
0.250 mol/Ls D) 4.00 mol/Ls E) 0.125 mol/Ls *** you must make the
mols equivalent in order to find the answer. Average and
Instantaneous Rates of Change Slide 30 Rate laws for Chemical
Reactions Next Slide In Chemical Kinetics, we can determine a RATE
LAW which is the quantitative relation between the reaction rate
and the concentrations of the reactants. This will prove to be
useful in determining new properties for Chemical Kinetics. Slide
31 Rate Laws for Chemical Reactions Next Slide As explained in the
previous slide, a RATE LAW is the quantitative relation between the
reaction rate and the concentrations of the reactants. A Rate Law
has the following form for the following reaction: Where k is the
RATE CONSTANT and x and y are the ORDERS of the reaction in respect
to their compounds. In other words, x is the order of the reaction
in respect to methane and y is the order of the reaction in respect
to oxygen. *** RATE is always in mol/Ls, thus, the rate constant
(k) will have different units for different orders. Slide 32 Rate
Laws for Chemical Reactions Next Slide Suppose the following
reaction was undergone: If we wanted to determine the RATE LAW for
the following reaction, we would need to obtain data
experimentally. This data would include concentrations of all
reactants and the INITIAL RATE of these reactants. The initial rate
is the instantaneous rate of change for a reaction at time equal to
zero. Suppose this data was obtained for the following reaction and
was put in the following chart: How can we determine the proper
rate law given this information? The method of Initial Rates! Slide
33 Rate Laws for Chemical Reactions Next Slide Data From Previous
Slide STEP 1Assume the rate law for the given reaction STEP 2Look
for concentrations that remained constant among experiments. STEP
3Create equations for the following experiments and solve for
order. Thus the appropriate RATE LAW is Slide 34 Rate Laws for
Chemical Reactions Next Slide Data From Previous Slide It is now
time to determine the value of the rate constant. In order to do
this, we must choose any values from a single experiment and solve
for k. Slide 35 Answer QUESTION 10 Given the following Chemical
Equations, Determine the Generic Rate law for each: 1) 2) 3) Rate
Laws for Chemical Reactions Slide 36 Next Question QUESTION 10
ANSWER 1) 2) 3) Rate Laws for Chemical Reactions Next Section Slide
37 Answer QUESTION 11 During a chemical reaction, three compounds
are combined simultaneously. Calculations are made and the order of
reactant A and B are determined. If the order of reactant A is 2
and the order of reactant B is 0, what is the order of reactant C
assuming the units on the rate constant are: Rate Laws for Chemical
Reactions Slide 38 Next Question QUESTION 11 ANSWER Thus the order
of reactant C is 3 Rate Laws for Chemical Reactions Next Section
Slide 39 Answer QUESTION 12 (pulled from midterm) A reaction, A + B
products, was studied using the method of initial rates. The
initial rate of consumption of B was measured in three different
experiments. Data are provided below: What are the correct units
for the rate constants, k for this reaction? Rate Laws for Chemical
Reactions Slide 40 Continue QUESTION 12 ANSWER *** We must first
determine the order. STEP 1Assume the rate law for the given
reaction STEP 2Look for concentrations that remained constant among
experiments. STEP 3Create equations for the following experiments
and solve for order. Thus the appropriate RATE LAW is Rate Laws for
Chemical Reactions Slide 41 Next Section QUESTION 12 ANSWER *** Now
that we have the proper Rate Law, we can use it to determine the
units on k. *** Thus the answer is C. Rate Laws for Chemical
Reactions Slide 42 Integrated Rate Laws Next Slide Because Rate is
equivalent to a differential expression, it is often the case that
an integrated form of the Rate Law can be achieved which allows
Chemists to use these equations for different types of
calculations. Slide 43 Integrate Rate Law Next Slide The Equations
achieved by integration of Rate Laws are as follows (These can be
found on your Data Sheet): Zero-Order Reactions First-Order
Reactions Second-Order Reactions Slide 44 Answer QUESTION 13 The
chemical equation describing the decomposition of Dinitrogen
Pentoxide is: The reaction is first-order and the rate constant is
k =.0682 min . If 1.00 mol of dinitrogen pentoxide is placed in a
2.00L reaction vessel at 352 C, then how long will it take for 25%
of the dinitrogen pentoxide to react? Integrate Rate Law Slide 45
Next Section QUESTION 13 ANSWER *** 25% used means 75% remains ***
Thus it will take 4.21 minutes. Integrate Rate Law Slide 46
Analysis of Concentration vs. Time Data Next Slide When dealing
with Orders of reactions, there is often two approaches used to
determine the order when data is given in respect to concentration
and time. These methods are the Graphical and Algebraic methods.
Slide 47 Analysis of Concentration vs. Time Data Next Slide For
each of the three orders that are discussed in this course, there
is an equation derived from its integrated equation. This equation
is simply solving for the rate constant and is useful when given
data because for one of the orders we should expect the rate
constant to remain constant. Slide 48 Analysis of Concentration vs.
Time Data Next Slide The Graphical Approach allows one to determine
the order simply by looking at the Graph. All you need to do is
remember a few rules and you should be fine at solving these types
of problems. For ZERO ORDER reactions, you should expect to see a
NEGATIVE linear slope with a plot of [A] vs. t For FIRST ORDER
reactions, you should expect to see a NEGATIVE linear slope with a
plot of ln[A] vs. t For SECOND ORDER reactions, you should expect
to see a POSITIVE linear slope with a plot of 1/[A] vs. t Slide 49
Answer QUESTION 14 Determine the order of the following reaction
(using both the graphical and algebraic method) given the following
data: Analysis of Concentration vs. Time Data Slide 50 Next Section
QUESTION 14 ANSWER Algebraic Method Graphical Method *** Thus this
reaction must be of order 2! Analysis of Concentration vs. Time
Data Slide 51 Half-Life Next Slide Half-life, is a period of time
it takes for a substance to decay to half of it original value.
Obviously, because this is a change in the amount of a substance
for a given time, this can easily be related to Rate of Reactions
in Chemical Kinetics. Slide 52 Half- Life Next Slide In this
course, we can achieve half-life formulae for each of the orders we
discuss. The derivation can be found in the course-notes: ZERO
ORDER FIRST ORDER SECOND ORDER Slide 53 Answer QUESTION 15 A
ancient rock is found on the coast of western Canada. This rock
seems to have deposits of Uranium, a nuclear decaying element,
assuming that the following reaction is a first order reaction. How
old is this rock if 15.7% of Uranium is present (assuming that the
amount of uranium originally on the rock was known) and the
half-life of Uranium is 245500 years? Half-Life Slide 54 Next
Section QUESTION 15 ANSWER First, we must determine the value of k
using the half-life formula for a first- order reaction: Second, we
must use the integrated first-order formula to calculate time t
when only 15.7% remains. Thus, the rock should be approximately
656563 years old! Half-Life Slide 55 Reaction Mechanisms Next Slide
The topics of Chemical Kinetics usually involve REACTION MECHANISMS
which consist of elementary processes that occur in a specific
order summing up to an overall reaction. These mechanisms all have
separate rates and thus are extremely important to study! A great
animation of Reaction Mechanisms can be found at
http://www.saskschools.ca/~bisstchem/modules/module4/lesso
n3/reactionmechanisms.htm Slide 56 Reaction Mechanisms Next Slide
The best way to understand a REACTION MECHANISM is to look at an
example. The following is the reaction mechanism between
2-bromo-2-methylpropane and a hydroxide ion: (CH ) C is an example
of an INTERMEDIATE. An intermediate can appear in the mechanism but
will not appear in the reaction. When you sum up the ELEMENTARY
PROCESSES, you achieve the overall reaction, which is what we are
most comfortable with! Slide 57 Reaction Mechanisms Next Slide As
stated earlier, ELEMENTARY PROCESSES are the most simplistic
processes usually involving a specific collision or a molecular
process. The following are just a few of the rate laws for
elementary processes: *** These rules only apply to Elementary
Processes! First-Order (Unimolecular) Second-Order (Bimolecular)
Third-Order (Termolecular) Slide 58 Reaction Mechanisms Next Slide
Two Cases to consider when determining the Rate Law from a
Mechanism: 1)Are the speeds of the reactions known? Is there a
distinctive slow reaction? If a slow reaction is determined we can
simply determine the Rate Law according to that step because it is
known that the Overall Rate is approximately equal to the Rate of
the slowest step! 2) If the speeds of the reaction arent given we
must do much math. We must pick a random step and determine the
Rate Law for that step and combine them with all other intermediate
steps. Slide 59 Reaction Mechanisms Next Slide While solving these
problems, we will encounter a case where we will have intermediates
that must be removed from the Rate Law. In order to do this, we
must use the STEADY STATE APPROXIMATION. This allows us to exchange
the rate of producing an intermediate with the rate of consuming an
intermediate (and vice versa). Think of the steady state as a
limit, the production of an intermediate is high at the beginning
of a reaction because the concentration of the reactants are high.
Once this concentration of the intermediate increases, so does the
consumption of the intermediate. But once the concentration of the
initial reactants decreases so does that speed of the production of
the intermediate which eventually will hit a steady state (a
constant value) where the production and consumption of the
intermediate is approximately equivalent. In the later reaction,
the consumption begins to get larger than the production depending
on the speed of the mechanisms. Slide 60 Answer QUESTION 16
TRUE/FALSE A Rate Law for a specific reaction allows one to
determine the order for each reactant in a reaction and also the
how reactants are actually converted into products. Reaction
Mechanisms Slide 61 Next Question QUESTION 16 ANSWER FALSE The
overall reaction does not tell us how a reactant is converted into
a product, it is a sum of everything that has occurred. An
elementary process will depict the actual conversion of a reactant
into a product. Reaction Mechanisms Next Section Slide 62 Answer
QUESTION 17 An Elementary Process is an event that depicts a
__________ or ___________. A)Molecular Process, Reaction Order
B)Collisional Event, Reaction Order C)Molecular Process, Reaction
Speed D) Molecular Process, Collisional Event E) Reaction Order,
Reaction Speed F) Reaction Speed, Collisional Event Reaction
Mechanisms Slide 63 Next Question QUESTION 17 ANSWER An Elementary
Process is an event that depicts a MOLECULAR PROCESS or COLLISIONAL
EVENT. A)Molecular Process, Reaction Order B)Collisional Event,
Reaction Order C)Molecular Process, Reaction Speed D) Molecular
Process, Collisional Event E) Reaction Order, Reaction Speed F)
Reaction Speed, Collisional Event Reaction Mechanisms Next Section
*** Reaction Order can be determined from an elementary process but
an elementary process does not determine the Reaction Order. ***
Reaction Speed is a property of molecules present in a elementary
process. Slide 64 Answer QUESTION 18 It is understood that the rate
of an elementary process is proportional to the total collision
rate which is proportional to the concentration of the reactants.
An elementary process is also proportional to the fraction of
collisions with sufficient kinetic energy and the fraction of
collisions with correct alignment. Which of the following
statements are true according to this information. 1) (Initially)
2) (for a non-zero ordered reaction) 3) If the concentration of the
Reactants were to increase, the Order of the Elementary Process
would be altered. 4) If the concentration of the Reactants were to
increase, the Initial Rate of an Elementary Process would increase.
Reaction Mechanisms Slide 65 Next Question QUESTION 18 ANSWER
1)FALSE *** concentrations of one reactant has no effect on the
concentration of another initially, once a reaction proceeds. this
would be true because of steady state. 2)TRUE 3)TRUE 4)TRUE
Reaction Mechanisms Next Section Slide 66 Answer QUESTION 19
Nitrogen monoxide reacts with hydrogen gas to produce nitrogen gas
and water vapour. The mechanism is believed to be: Step 1: 2 NO N 2
O 2 Step 2: N 2 O 2 + H 2 N 2 O + H 2 O Step 3: N 2 O + H 2 N 2 + H
2 O What is the overall balanced equation and any reaction
intermediates? Reaction Mechanisms Slide 67 Next Question QUESTION
19 ANSWER To find the overall balanced equation, cross out
substances that appear in equal numbers on both sides of the
reaction and add together like items on the same side of the
equation: Step 1: 2 NO N 2 O 2 Step 2: N 2 O 2 + H 2 N 2 O + H 2 O
Step 3: N 2 O + H 2 N 2 + H 2 O Net Reaction: 2 NO + 2 H 2 N 2 + 2
H 2 O To identify the reaction intermediates, look for substances
that first appear on the product side of the equation, but then
appear in the next step as a reactant. Intermediates: N 2 O 2 and N
2 O. Reaction Mechanisms Next Section Slide 68 Answer QUESTION 20
Determine the Rate of Reaction for the following reaction
mechanism: Overall Reaction: 2 NO 2 + F 2 2NO 2 F Step 1: NO 2 + F
2 NO 2 F + F (slow) Step 2: NO 2 + F NO 2 F (fast) Reaction
Mechanisms Slide 69 Next Question QUESTION 20 ANSWER Overall
Reaction: 2 NO 2 + F 2 2NO 2 F Step 1: NO 2 + F 2 NO 2 F + F (slow)
Step 2: NO 2 + F NO 2 F (fast) Rate = K[NO 2 ][F 2 ] *** Since no
intermediates are present in the rate determining step, it is
simply the rate law for that step. To determine the rate law, you
must apply the same laws for elementary processes. Reaction
Mechanisms Next Section The slowest step of any mechanism is often
referred to as the RATE DETERMINING STEP because the rate law can
be derived from that step! Slide 70 Answer QUESTION 21 Determine
the Rate of Reaction for the following reaction mechanism: Overall
Reaction: H 2 + Br 2 2HBr Step 1: Br 2 2Br (fast) Step 2:Br + H 2
HBr + H (slow) Step 3:H + Br HBr (fast) Reaction Mechanisms Slide
71 Next Section QUESTION 21 ANSWER Overall Reaction: H 2 + Br 2
2HBr Step 1: Br 2 2Br (fast) Step 2:Br + H 2 HBr + H (slow) Step
3:H + Br HBr (fast) In this problem an intermediate exists, Because
of that, it is a two step problem. First, we will determine the
Rate of the slowest step: Then we will determine the rate of any
intermediates in our initial rate: ****** Reaction Mechanisms The
slowest step of any mechanism is often referred to as the RATE
DETERMINING STEP because the rate law can be derived from that
step! Slide 72 How Does Temperature Affect Reaction Rate? Next
Slide As we discussed earlier, Temperature has a large effect on
the rate of chemical reactions. It is usually the case that
increasing temperature will result in a faster rate of reaction. In
this section we will discuss the affects of temperature and get
into some Collision Theory. Slide 73 How Does Temperature Affect
Reaction Rate? Next Slide By definition, TEMPERATURE is the average
measure of KINETIC ENRGY or molecules in a system. From Question
18, we briefly discussed the proportionalities of Rate: it is
observed that rate is proportional to three important factors:
1)The frequency of collision (How often collision take place).
2)The number of collision that are properly aligned over the total
number of collisions. 3)The number of collision that have enough
kinetic energy for the reaction to undergo over the total number of
collisions. The third point is very important when talking about
temperature because we know that if we increase temperature, which
will increase the average kinetic energy in a system, we will
expect the number of collisions that have enough kinetic energy to
produce a proper change to increase because there is more kinetic
energy in the system. Thus, this is why when temperature is
increased, rate is also increased. Slide 74 How Does Temperature
Affect Reaction Rate? Next Slide When a collision is undergone, it
is important to note that there is often an activated complex
associated with each collision for all molecules. The ACTIVATED
COMPLEX is the short-lived, high-energy complex in a chemical
reaction that persists while old bonds are breaking and new bonds
are forming. This activated complex deals with the conversion of
kinetic energy from the reaction to potential energy in the
complex. *** It is important to note that an activated complex will
be formed whether or not a sufficient amount of kinetic energy is
present. BUT, if the kinetic energy for a given collision isnt
greater than or equal to the forward activation energy, the
activated complex will be converted back into reactant form. Slide
75 How Does Temperature Affect Reaction Rate? Next Slide There are
two activation energies associated for a reaction. The first is the
FORWARD activation energy, which would be the activation energy
seen on the left of the potential energy diagram, and the second is
the REVERSE activation energy, which would be seen on the right of
the potential energy diagram. The relationship between these two
energies can be quantified by the following equation which includes
the enthalpy of the reaction (the change in energy between products
and reactants). Slide 76 How Does Temperature Affect Reaction Rate?
Next Slide Svante Arrhenius was the first to quantify a constant k
for the three proportionalities of Rate. His efforts have been
quantified in the following equation similar to the
Clausius-Cloperon equation. This Arrhenius equation dictates a
relationship of the activation energy for a reaction which is said
to be determined by the slope of the plot of ln(k) versus (1/T).
Slide 77 Answer QUESTION 22 The Activation Complex is a
____________, ______________ complex that is formed when the
____________ energy of the collisions has been converted into the
___________ energy stored within complex. 1)Potential 2)Low-energy
3)Short-lived 4)Kinetic 5)Long-lived 6)High-energy *** Determine
the list of numbers, in order, that will satisfy the following
definition of the Activated Complex. Reaction Mechanisms Slide 78
Next Question QUESTION 22 ANSWER The Activation Complex is a
Short-lived, High-energy complex that is formed when the Kinetic
energy of the collisions has been converted into the Potential
energy stored within complex. 1)Potential 2)Low-energy
3)Short-lived 4)Kinetic 5)Long-lived 6)High-energy ***(3, 6, 4, 1)
How Does Temperature Affect Reaction Rate? Next Section Slide 79
Answer QUESTION 23 For a specific reaction, the forward activation
energy is 125.00 KJ/mol and the reverse activation energy 13563
J/mol. Determine the enthalpy of this reaction and dictate whether
it is endothermic or exothermic. How Does Temperature Affect
Reaction Rate? Slide 80 Next Question QUESTION 23 ANSWER Since the
enthalpy for this reaction is positive, this reaction is
ENDOTHERMIC. How Does Temperature Affect Reaction Rate? Next
Section Slide 81 Answer QUESTION 24 Consider the following Data: k
= 1.25 @ T = 286K k = 2.67 @ T = 354K Determine the activation
energy from this data by the Arrhenius Equation. How Does
Temperature Affect Reaction Rate? Slide 82 Next Section QUESTION 24
ANSWER Thus the Activation Energy is 9.4 KJ/mol How Does
Temperature Affect Reaction Rate? Slide 83 Catalysts Next Slide As
discussed earlier, a Catalyst is very important in a reaction
because it lowers the activation energy of a reaction. In biology,
this is extremely important because without these necessity
molecules, our bodies wouldnt be able to function properly and life
as we know it would be completely different. Slide 84 Catalysts
Next Slide During a reaction, a catalyst is usually noted when it
starts as a reactant and is produced as a product. Thus, a major
role in determining the presence of a catalyst is to show that it
isnt used up in a reaction, it must remain present in the overall
reaction. Though the mechanism of a reaction involving a catalyst
may show the use of the catalyst, it must in the end reproduce the
catalyst. A major calculation involving catalysts is to show how
much faster the reaction is with or without the catalyst. Slide 85
Catalysts Next Slide As the course notes state, DO NOT ASSUME THE
RATE- DETERMINING STEP IS THE STEP WITH THE HIGHEST ACTIATION
ENERGY!!! The rate determining step is always the elementary
process that has the transition state of highest energy! That is,
given a potential energy diagram, the step that has the highest
amount of potential energy, is the step that is the rate
determining step! Rate-Determining Step Slide 86 Answer QUESTION 25
Determine how many intermediates are in the following Potential
energy diagram and also determine the Rate-Determining Step:
Reaction Mechanisms Slide 87 Next Question QUESTION 25 ANSWER
Reaction Mechanisms Thus there are 3 intermediates Dont get
confused with activated complexes! Rate Determining Step Slide 88
Answer QUESTION 26 Given the following reactions, which ones
contain a catalyst? 1)2) Step 1: 2 NO N 2 O 2 Step 2: N 2 O 2 + H 2
N 2 O + H 2 O Step 3: N 2 O + H 2 N 2 + H 2 O 3)4) Reaction
Mechanisms Slide 89 Next Question QUESTION 26 ANSWER 1) No
Catalysts present 2) No Catalysts present 3) Catalyst present 4)
Catalyst present Reaction Mechanisms Slide 90 Answer QUESTION 27 A
catalyst decreases the activation energy of a given reaction by
exactly 17 kJ/mol. By what factor does the reaction rate increase
at 25 o C when the catalyst is used? Assume that the Arrhenius
pre-exponential factor, A, is the same for the catalyzed and
uncatalyzed reactions. Reaction Mechanisms Slide 91 START OVER
QUESTION 27 ANSWER First, lets suppose the uncatalyzed activation
energy is x, thus the catalyzed activation energy is x-17. Reaction
Mechanisms
