ch 13 chemical kinetics - dsu college of agriculture ... · elementary step 1: no + no n 2 o 2...
TRANSCRIPT
![Page 1: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/1.jpg)
Ch 13 Chemical Kinetics
Modified by Dr. Cheng-Yu Lai
![Page 2: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/2.jpg)
Outline
1. Meaning of reaction rate
2. Reaction rate and concentration
3. Writing a Rate Law
4. Reactant concentration and time
5. Reaction rate and temperature
6. Catalysis and Reaction mechanisms
![Page 3: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/3.jpg)
A B
time
We want to know how fast is this reaction ? Reaction Rate = ?
![Page 4: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/4.jpg)
Reaction Rate
12
12 ][][
tt
ttimeatAttimeatARate
t
ARate
][
The change in concentration of a reactant or product per unit of time.
Rate A = - = - (5-40)/60 [A]
t
Rate B = = (35-0)/60 [B]
t
![Page 5: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/5.jpg)
© 2014 Pearson Education, Inc.
Reaction Rate and Stoichiometry
• In most reactions, the coefficients of the balanced equation are not all the same.
H2 (g) + I2 (g) 2 HI(g)
• For these reactions, the change in the number of molecules of one substance is a multiple of the change in the number of molecules of another. – For the above reaction, for every 1 mole of H2 used, 1
mole of I2 will also be used and 2 moles of HI made.
– Therefore, the rate of change will be different.
• To be consistent, the change in the concentration of each substance is multiplied by 1/coefficient.
![Page 6: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/6.jpg)
© 2014 Pearson Education, Inc.
H2 (g) + I2 (g) 2 HI (g)
Using [H2], the
instantaneous rate
at 50 s is as follows:
Using [HI], the
instantaneous rate
at 50 s is as follows:
![Page 7: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/7.jpg)
General Form of the Rate Relationship
• For a reaction where aA + bB cC + dD
td
D
tc
C
tb
B
ta
Arate
][][][][
• N2 (g) + 3H2 (g) 2NH3 (g)
• If the N2 is disappearing at 0.10 mol/L-min, the H2 is disappearing at the rate of 0.30 mol/L-min and ammonia is appearing at a rate of 0.20 mol/L-min
Example - Formation of Ammonia
t2
]NH[
t3
]H[
t
]N[rate 322
![Page 8: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/8.jpg)
Reaction Rate Relationship between Reactants and Products Concentration
• N2O5 (g) 2NO2 (g) + ½O2 (g)
– What happens to the concentrations with time? • [N2O5] decreases
• [NO2] and [O2] increase
– Mathematically, we can express the concentration change relationship between reactants and products as
A short reminder Reaction Rate : The change in concentration of a reactant or product per unit of time.
2
1
][
2
][][ 22
52
ONOON
t
Crate
][
![Page 9: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/9.jpg)
![Page 10: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/10.jpg)
![Page 11: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/11.jpg)
Curved Rather than Straight Line Tell Us That.....
I. Rate is not Constant Throughout Reaction- just like 5K racing
II. Reaction Rate is Higher with Higher Concentration
(-) slope means concentration is decreasing, less steep
![Page 12: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/12.jpg)
Rate and Each Reactant Concentration MORE CHANCE FOR MOLECULES TO COLLIDE
![Page 13: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/13.jpg)
Rate and Rate Law Differentiated Rate Law : expressed the relationship between the concentration of reactants and the rate of reaction. The differentiated Rate Law is usually just called rate law.
Rate unt is always in mol/L-time
There are three orders: The order with respect to A - x The order with respect to B - y The overall order (x+y)
• X,Y Determined by experimental data- Stoichiometry of equation is irrelevant
• Only reactants in rate law
![Page 14: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/14.jpg)
Writing a Rate Law
O2
NO
NO2
![Page 15: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/15.jpg)
Writing a Rate Law
![Page 16: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/16.jpg)
Writing a Rate Law
Overall order =3
![Page 17: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/17.jpg)
Writing a Rate Law
Next , Concentration as a Function of Time from the rate and rate law equations
![Page 18: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/18.jpg)
Chapter 12/18 © 2012 Pearson Education, Inc.
Integrated Rate Law for a First-
Order Reaction A product(s)
rate = k[A]
Calculus can be used to derive an integrated rate law.
[A]
t - = k[A]
x
y ln = ln(x) - ln(y) Using:
[A]t
[A]0 ln = -kt
ln[A]t = -kt + ln[A]0
y = mx + b
[A]t concentration of A at time t
[A]0 initial concentration of A
![Page 19: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/19.jpg)
Chapter 12/19 © 2012 Pearson Education, Inc.
Integrated Rate Law for a First-
Order Reaction
Slope = -k
k = 0.0017
650 s - 150 s
-5.02 - (-4.17) = -0.0017
s 1
Calculate the slope:
s 1
2N2O5(g) 4NO2(g) + O2(g)
rate = k[N2O5]
![Page 20: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/20.jpg)
Chapter 12/20 © 2012 Pearson Education, Inc.
Half-Life of a First-Order
Reaction Half-Life: The time required for the reactant
concentration to drop to one-half of its initial value
A product(s)
rate = k[A]
[A]t
[A]0 ln = -kt
t = t1/2
= t1/2
[A] 2
[A]0
= -kt1/2 1
2 ln t1/2 =
k
0.693 or
![Page 21: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/21.jpg)
![Page 22: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/22.jpg)
Chapter 12/22 © 2012 Pearson Education, Inc.
Half-Life of a First-Order
Reaction
t1/2 = k
0.693
For a first-order
reaction, the half-life is
independent of the initial
concentration.
Each successive half-life
is an equal period of
time.
![Page 23: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/23.jpg)
First-Order Reactions
What is the half-life of N2O5 if it decomposes with a rate
constant of 5.7 x 10-4 s-1?
t½
ln2
k =
0.693
5.7 x 10-4 s-1 = = 1200 s = 20 minutes
kt = ln[A]0 – ln[A]
t = ln[A]0 – ln[A]
k = 66 s
ln [A]0
[A]
k =
ln 0.88 M
0.14 M
2.8 x 10-2 s-1 =
The reaction 2A B is first order in A with a rate
constant of 2.8 x 10-2 s-1 at 800C. How long will it take for A
to decrease from 0.88 M to 0.14 M ?
ln[A] = ln[A]0 - kt [A]0 = 0.88 M [A] = 0.14 M
![Page 24: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/24.jpg)
Zero Order Reactions
• For a zero order reaction A products
• Note that the half life of a zero order reaction does depend on the initial concentration of reactant
t.vs]A[:linear
k2
]A[t
kt]A[]A[
k]A[kRate
02/1
0
0
Second-Order Reactions
tvsA
linear
Akt
ktAA
.][
1:
][
1
][
1
][
1
0
2/1
0
For A products, Rate = k[A]2
![Page 25: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/25.jpg)
Chapter 12/25 © 2012 Pearson Education, Inc.
![Page 26: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/26.jpg)
Chapter 12/26 © 2012 Pearson Education, Inc.
Zeroth-Order Reactions
A plot of [A] versus time
gives a straight-line fit and
the slope will be -k.
![Page 27: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/27.jpg)
![Page 28: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/28.jpg)
![Page 29: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/29.jpg)
![Page 30: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/30.jpg)
Factors for Reaction Rate A-> B
1.Concentration
• Rate = -[A]/t
• Rate law; Rate = k[A]x
2. Temperature and Rate
• Found in the Rate Law Constant, k
![Page 31: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/31.jpg)
Temperature and Rate
• Generally, as temperature increases, so does the reaction rate.
• This is because k ,rate constant, is temperature dependent.
![Page 32: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/32.jpg)
Arrhenius Equation
Svante Arrhenius developed a mathematical relationship between k and Ea:
where A is the frequency factor, a number that represents the likelihood that collisions would occur with the proper orientation for reaction.
The greater (Ea/RT) is;
the smaller k is;
slower reaction rate !
![Page 33: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/33.jpg)
Arrhenius Equation Taking the natural
logarithm of both sides, the equation becomes
1 RT
y = mx + b When k is determined experimentally at several temperatures, Ea can be calculated from the slope of a plot of ln k vs. 1/T.
The Arrhenius equation is similar in nature and can be used for two k values and two temperatures
Ea may then be calculated
211
2 11ln
TTR
E
k
k a
![Page 34: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/34.jpg)
![Page 35: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/35.jpg)
Activation Energy
• In other words, there is a minimum amount of energy required for reaction: the activation energy, Ea.
• Just as a ball cannot get over a hill if it does not roll up the hill with enough energy, a reaction cannot occur unless the molecules possess sufficient energy to get over the activation energy barrier.
![Page 36: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/36.jpg)
Reaction Coordinate Diagrams
• It shows the energy of the reactants and products (and, therefore, E).
• The high point on the diagram is the transition state.
• The species present at the transition state is called the activated complex.
• The energy gap between the reactants and the activated complex is the activation energy barrier.
![Page 37: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/37.jpg)
Reaction Diagram and Catalyst
![Page 38: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/38.jpg)
A catalyst is a substance that increases the rate of a chemical
reaction without itself being consumed.
k = A • exp( -Ea / RT ) Ea k
ratecatalyzed > rateuncatalyzed
Ea < Ea ‘
Uncatalyzed Catalyzed
![Page 39: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/39.jpg)
Homogeneous and Heterogeneous Catalysts
• Homogeneous catalyst: catalyst existing in the same phase as the
reactants.
• Heterogeneous catalysis: catalyst existing in a different phase
than the reactants.
– The previous section gave an example of a homogeneous
catalyst since the catalyst Br2 was in the same phase as the
hydrogen peroxide.
• The catalytic hydrogenation of ethylene is an example of a
heterogeneous catalysis reaction:
• ENZYMES (biological catalysts)
– They are proteins (large organic molecules that are composed
of amino acids).
– Slotlike active sites. The molecule fits into this slot and
reaction proceeds. Poisons can block active site or reduce
activity by distorting the active site.
)g(CHCH)g(H)g(CHCHPt
33222
![Page 40: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/40.jpg)
Factors that Influence the Rate of Reaction
• Concentration of reactants ,
• Types of reactions
• Temperature
• Presence of a catalyst
• Reaction mechanism
![Page 41: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/41.jpg)
Sequence of Steps in Studying a Reaction Mechanism
![Page 42: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/42.jpg)
Reaction Mechanisms
The overall progress of a chemical reaction can be represented
at the molecular level by a series of simple elementary steps
or elementary reactions.
The sequence of elementary steps that leads to product
formation is reaction mechanism.
2NO (g) + O2 (g) 2NO2 (g)
N2O2 is detected during the reaction!
Elementary step: NO + NO N2O2
Elementary step: N2O2 + O2 2NO2
Overall reaction: 2NO + O2 2NO2
+
![Page 43: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/43.jpg)
Elementary step 1: NO + NO N2O2
Elementary step 2: N2O2 + O2 2NO2
Overall reaction 1+ 2: 2NO + O2 2NO2
+
Intermediates are species that appear in a reaction
mechanism but not in the overall balanced equation.
An intermediate is always formed in an early elementary step
and consumed in a later elementary step.
The molecularity of a reaction is the number of molecules
reacting in an elementary step.
• Unimolecular reaction – elementary step with 1 molecule
• Bimolecular reaction – elementary step with 2 molecules
• Termolecular reaction – elementary step with 3 molecules
![Page 44: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/44.jpg)
The rate-determining step is the slowest step in the
sequence of steps leading to product formation.
Mechanism Involving Multiple Steps
![Page 45: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/45.jpg)
Chapter 12/45 © 2012 Pearson Education, Inc.
Reaction Mechanisms-
Molecularity Unimolecular Reaction
O3*(g) O2(g) + O(g)
Bimolecular Reaction
O3(g) + O(g) 2O2(g)
![Page 46: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/46.jpg)
Rate Laws for Elementary
Reactions The rate law for an elementary reaction follows
directly from its molecularity because an elementary
reaction is an individual molecular event.
Termolecular Reaction
O3*(g) O2(g) + O(g) rate = k[O3]
Unimolecular Reaction
rate = k[O3][O] O3(g) + O(g) 2O2(g)
Bimolecular Reaction
O(g) + O(g) + M(g) O2(g) + M(g) rate = k[O]2[M]
![Page 47: Ch 13 Chemical Kinetics - DSU College of Agriculture ... · Elementary step 1: NO + NO N 2 O 2 Elementary step 2: N 2 O 2 + O 2 2NO 2 Overall reaction 1+ 2: 2NO + O 2 2NO 2 + Intermediates](https://reader033.vdocuments.us/reader033/viewer/2022042022/5e79334284ff61111f69cfc0/html5/thumbnails/47.jpg)
© 2014 Pearson Education, Inc.
Insert Table 13.2