Post on 15-Dec-2015
13-1CHEM 102, Spring 2014, LA TECH
Instructor: Dr. Upali Siriwardane
e-mail: upali@latech.edu
Office: CTH 311
Phone 257-4941
Office Hours: M,Tu, W,Th,F 9:00-11:00 am ;
Test Dates: 9:30-10:45 am., DAVH 209
Chemistry 102(60) Summer 2014
July 21, 2014 (Test 1): Chapter 13
July 28, 2014 (Test 2): Chapter 14
August 5, 2014 (Test 3): Chapter 15 &16
August 13, 2014 (Test 4) Chapter 17
August 14, 2014 (Make-up test) comprehensive:
Chapters 13-17
13-2CHEM 102, Spring 2014, LA TECH
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
13-3CHEM 102, Spring 2014, LA TECH
Why Study Rates of Reactions?1) Rates show us how fast/slow a reaction would
take place.
2) We need make some reactions go faster.
3) Some reactions needed to be slowed down.
4) We need the conceptual back ground of the “factors” that would change the rate of a reaction
5) In this chapter we will go through models and the theories dealing with reaction rates (Chemical Kinetics)
13-4CHEM 102, Spring 2014, LA TECH
How do you measure rates?
• 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
H2 + I2 --> 2 HI
13-5CHEM 102, Spring 2014, LA TECH
Reaction of cis-platin with Water
Substitution reaction
13-6CHEM 102, Spring 2014, LA TECH
Disappearance of ColorIntensity of Color is proportional to amount of reactant
13-7CHEM 102, Spring 2014, LA TECH
13-8CHEM 102, Spring 2014, LA TECH
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 disappearance.
rate = (D[NO2]/ D t = - 4/2 D[N2O5]/ D t
D[O2]/ D t = - 1/2 D[N2O5]/ D t
13-9CHEM 102, Spring 2014, LA TECH
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
13-10CHEM 102, Spring 2014, LA TECH
1) What is the rate of a chemical reaction? (Describe in your own words and then in equation)
a A ----> b B + c C
13-11CHEM 102, Spring 2014, LA TECH
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)
13-12CHEM 102, Spring 2014, LA TECH
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)
13-13CHEM 102, Spring 2014, LA TECH
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)
13-14CHEM 102, Spring 2014, LA TECH
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)
13-15CHEM 102, Spring 2014, LA TECH
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?
13-16CHEM 102, Spring 2014, LA TECH
3) What are the differences between average and instantaneous reaction rates? Refer to graph in new concepts.
13-17CHEM 102, Spring 2014, LA TECH
4) Why is instantaneous rates of N2O5 and NO2 are negative and positive respectively?
13-18CHEM 102, Spring 2014, LA TECH
2 N2O5(g) -----> 4 NO2 (g) + O2 (g)Graphing Kinetics Data
Average rate =
13-19CHEM 102, Spring 2014, LA TECH
Graph
13-20CHEM 102, Spring 2014, LA TECH
Graph in Problem 7
0
0.005
0.01
0.015
0.02
0 50 100 150 200
Series1
Time / min [N2O5] / moldm-3 0 0.01756
20 0.0093340 0.0053160 0.0029580 0.00167
100 0.00094160 0.00014
5) At what time the reaction is complete?
13-21CHEM 102, Spring 2014, LA TECH
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-3
min-1
tf - ti
0-20 = - ½ [0.00933] - [0.01756] = 2.06 x 10-4
mol dm-3
min-1
20 - 0
20-40 =
40-60 =
60-80 =
13-22CHEM 102, Spring 2014, LA TECH
7) How does reaction rate vary with time in the graph? Consider the decomposition of
N2O5.
0
0.005
0.01
0.015
0.02
0 50 100 150 200
Series1
13-23CHEM 102, Spring 2014, LA TECH
a) Temperature
b) Concentration
c) Catalysts
d) Particle size of solid reactants
Factors that affect rates of a chemical reactions
13-24CHEM 102, Spring 2014, LA TECH
8)What are the main factors that affect a rate of a chemical reaction?
13-25CHEM 102, Spring 2014, LA TECH
Effect of Particle Size on Rate
13-26CHEM 102, Spring 2014, LA TECH
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?