Transcript chem 102

Chemistry 102(01) Fall 2013
Instructor: Dr. Upali Siriwardane
e-mail: [email protected]
Office: CTH 311
Phone 257-4941
Office Hours: M,W 8:00-9:30 & 11:00-12:30 am;
Tu,Th, F 8:00 - 10:00 am., or by appointment.
Test Dates:
September 24, 2013 (Test 1): Chapter 13
October 17,
2013 (Test 2): Chapter 14 &15
November 12, 2013 (Test 3) Chapter 16 &17
November 14, 2013 (Make-up test) comprehensive:
Chapters 13-17 10:00-11:15 am., CTH 328
CHEM 102, Fall 2013, LA TECH
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Chapter 13. Chemical Kinetics
13.1 Catching Lizards
563
13.2 The Rate of a Chemical Reaction
564
13.3 The Rate Law: The Effect of Concentration
on Reaction Rate
569
13.4 The Integrated Rate Law: The Dependence of
Concentration on Time
573
13.5 The Effect of Temperature on Reaction Rate 581
13.6 Reaction Mechanisms
588
13.7 Catalysis
593
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Why Study Rates of Reactions?
1) Rates show us how fast/slow a reaction would
2)
3)
4)
5)
take place.
We need make some reactions go faster.
Some reactions needed to be slowed down.
We need the conceptual back ground of the
“factors” that would change the rate of a
reaction
In this chapter we will go through models and
the theories dealing with reaction rates
(Chemical Kinetics)
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How do you measure rates?
H2 + I2 -->
2 HI
• Rates are related to the time it required to decay
reactants or form products.
• The rate reaction = change in concentration of
reactants/products per unit time
• Average rate
rate of reaction = – D[reactant]/Dt
• Instantaneous rate
rate of reaction = – d[reactant]/dt
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Reaction of cis-platin with Water
Substitution reaction
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Disappearance of Color
Intensity of Color is proportional to amount of
reactant
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Rate of Appearance & Disappearance
is different from Reaction Rates
2 N2O5(g) -----> 4 NO2 (g) + O2 (g)
Disappearance is based on reactants
rate = -(D[N2O5]/ D t
Appearance is based on products
rate = D[NO2]/ D t
rate = D[O2]/ D t
Converting rates of Appearance and disapperence.
rate = (D[NO2]/ D t = - 4/2 D[N2O5]/ D t
D[O2]/ D t = - 1/2 D[N2O5]/ D t
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Measuring Reaction Rate
a A --> b B
Based on reactants
rate = -(1/a) D[A]/ D t
Based on products
rate = +(1/b) D[B]/ D t
D[A]= [A]f - [A]I Change in A
D t= tf - ti Change in t
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1) What is the rate of a chemical reaction? (Describe
in your own words and then in equation)
a A ----> b B + c C
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2) Answer the following Given the chemical reaction:
2 N2O5 ----> 4 NO2 + O2
a) What’s the rate of disappearance ( or decomposition)
N2O5? (Equation)
b) What are the rates of appearance of NO2 and O2?
(Equations)
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2) Answer the following Given the chemical reaction:
2 N2O5 ----> 4 NO2 + O2
c) What are the rates of reaction based on N2O5, NO2 ,
and O2? (Equations)
d) Are the rates of decomposition based on N2O5, and
formation based on , NO2 , and O2 equal?
(Explanation)
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2) Answer the following Given the chemical reaction:
2 N2O5 ----> 4 NO2 + O2
e) Are the rate of reaction based on N2O5, NO2 , and O2
equal? (Equations and explanation)
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2) Answer the following Given the chemical reaction:
2 N2O5 ----> 4 NO2 + O2
e) Are the rate of reaction based on N2O5, NO2 , and O2
equal? (Equations and explanation)
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3) What are the differences between average and
instantaneous reaction rates? Refer to graph in new
concepts.
4) Why is instantaneous rates of N2O5 and NO2 are
negative and positive respectively?
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3) What are the differences between average and
instantaneous reaction rates? Refer to graph in new
concepts.
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4) Why is instantaneous rates of N2O5 and NO2 are
negative and positive respectively?
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Graphing Kinetics Data
2 N2O5(g) -----> 4 NO2 (g) + O2 (g)
Average rate =
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Graph
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Graph in Problem 7
Time / min
[N2O5] / moldm-
0
20
40
60
80
100
160
0.01756
0.00933
0.00531
0.00295
0.00167
0.00094
0.00014
3
0.02
0.015
0.01
Series1
0.005
0
0
50
100
150
200
5) At what time the reaction is complete?
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Graph in Problem 7
6) Plot this data using excel and attach the graph and do the
calculations using the spread sheet: What are the rates of
reaction between following min intervals?
0-20 = - ½ [N2O5]f - [N2O5]i
= 2.06 x 10-4 mol dm-3min-1
tf - ti
0-20 = - ½ [0.00933] - [0.01756] = 2.06 x 10-4 mol dm-3min-1
20 - 0
20-40 =
40-60
=
60-80
=
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7) How does reaction rate vary with time in the
graph? Consider the decomposition of N2O5.
0.02
0.015
0.01
Series1
0.005
0
0
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50
100
150
200
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Factors that affect rates of
a chemical reactions
a) Temperature
b) Concentration
c) Catalysts
d) Particle size of solid reactants
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8)What are the main factors that affect a rate of a
chemical reaction?
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Effect of Particle Size on Rate
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9) In the graph below, what are the main features
regarding rates based on reactants and products
and their stoichiometric coefficients and what
does it mean by kinetic and equilibrium regions?
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