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Lecture April 10
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Next HW and Quiz Chapter 15 due
Monday, April 22rd
Chapter 15 - Kinetics
Chapter 15 HW and Quiz will be postedthis weekend
All regrades due by Friday, April 19
Chapter 15 -Chemical Kinetics
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Reaction rate = concentration change/time =![ ]/!t
N2(g) + O2(g) "2NO(g)
Relationships between di#erent ratemonitors:
Rate 1 = ![O2]/!t
Rate 2 = ![N2]/!t
Rate 3 = ![NO]/!t
Rate 1 = Rate 2= -1/2 Rate 3
Graphical Representation
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Types of rates: ![ ]/!t
Average reaction rate - over an interval of timeFig. 15.3
Instantaneous rate -tangent to the curve at a given
time - Fig. 15.4
!Initial rate - tangent to the curve at t=0Fig. 15.6
Plot [ ] as a function of time - Fig. 15.3
Example of Data
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Rate![O2]/!t
1.6 x 10-5
1.1 x 10-5
0.8 x 10-5
(2.2 x 10-5)/4 =
0.55 x 10-5
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Determining the Rate LawUsing the Initial Rate
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Half [NO] rate is1/4
Half [O2] ratehalf
heck - half bothrate 1/8
Rate = k[NO]2[O2]k is the rate constant
= 2.0 M-2s-1
Table 15.3
1 0.0100 0.0100 2.0 x 10-6
2 0.0100 0.0050 1.0 x 10-6
3 0.0050 0.0100 5.0 x 10-7
4 0.0050 0.0050 2.5 x 10-7
Experimen [NO]o [O2] Initial
2NO(g) + O2(g) "2NO2(g)
Forms of Rate Equations
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Rate = k [A]
Rate = k
Rate = k [A]2
Rate = k [A] [B]
zero order
first order
second order
second order overallfirst order in A, first order in B
Rate = k [A]2[B]third order overall
second in A, first in B
!
!
Integrated Rate Laws
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Determining the order of the reaction
Rate = -![A]/!t = k [A]
[A] = [Ao] e-kt k is the rate constant
First Order
First Order Reaction Graphically
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2N2O5(g)"4NO2(g) + O2(g)
-k = {(-4.595) - (-4.255)}/ (400-200) = -1.7x10-3
k = 1.7 x 10-3 s-1
