13-1CHEM 102, Fall 2013, LA TECH

Instructor: Dr. Upali Siriwardane

e-mail: upali@coes.latech.edu

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:

Chemistry 102(01) Fall 2013

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

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Chapter 13. Chemical Kinetics 13.1 Catching Lizards 56313.2 The Rate of a Chemical Reaction 56413.3 The Rate Law: The Effect of Concentration on Reaction Rate 56913.4 The Integrated Rate Law: The Dependence of Concentration on Time 57313.5 The Effect of Temperature on Reaction Rate

58113.6 Reaction Mechanisms 58813.7 Catalysis

593

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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)

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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

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Reaction of cis-platin with WaterSubstitution reaction

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Disappearance of ColorIntensity 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

13-9CHEM 102, Fall 2013, 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, Fall 2013, 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, Fall 2013, 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)

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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)

13-14CHEM 102, Fall 2013, 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)

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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.

13-17CHEM 102, Fall 2013, LA TECH

4) Why is instantaneous rates of N2O5 and NO2 are negative and positive respectively?

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2 N2O5(g) -----> 4 NO2 (g) + O2 (g)Graphing Kinetics Data

Average rate =

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Graph

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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?

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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-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 =

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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

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a) Temperature

b) Concentration

c) Catalysts

d) Particle size of solid reactants

Factors that affect rates of a chemical reactions

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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?