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

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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

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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.

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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

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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?

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?