Chemistry 102(060) Summer 2012 CTH 328 11:30-12:45 am Instructor: Dr. Upali Siriwardane e-mail: upali@latech.edu Office: CTH 311 Phone 257-4941 Office Hours: M,W 8:00-9:00 & 11:00-12:00 am; Tu,Th,F 8:00-10:00 am.. Exams: 9:30-10:45 am, CTH 328. July 16, 2012 (Test 1): Chapter 13 July 23, 2012 (Test 2): Chapter 14 &15 July31, 2012 (Test 3): Chapter 16 &17 August 8, 2012 (Test 4): Chapter 18 Optional Comprehensive Final Exam: August 9, 2012 : Chapters 13, 14, 15, 16, 17, and 18 13-1 Syllabus and Grading 1) Four tests 600 (60%) 2) 11 Group-Homeworks (GHW) 200 (20%) 3) 20 Quizzes and attendance 100 (10%) 4) 3 OWL assignments 100 (10%) 1000 (100%) Bonus 1) Bonus Assignment 40 (4%) 2) Bonus Point-class participation 10 (1%) Complete the syllabus questionnaire 13-2 GHW# 1: Chapter 13 Chemical Kinetics: Reaction Rates 13-3 Chapter 13. Chemical Kinetics 13.1 Reaction Rate 13.2 Effect of Concentration on Reaction Rate 13.3 Rate Law and Order of Reaction 13.4 A Nanoscale View: Elementary Reactions 13.5 Temperature and Reaction Rate: The Arrhenius Equation 13.6 Rate Laws for Elementary Reactions 13.7 Reaction Mechanisms 13.8 Catalysts and Reaction Rate 13.9 Enzymes: Biological Catalysts 13-10Catalysis in Industry 13-4 1
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 understand 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) Reaction of cis-platin with Water Substitution reaction 13-5 13-6 Disappearance of Color How do you measure rates? Intensity of Color is proportional to amount of reactant 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 13-7 13-8 2
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= t f - t i Change in t Rate of Appearance & Disappearance is different from Reaction Rates 2 N 2 O 5 (g) -----> 4 NO 2 (g) + O 2 (g) Disappearance is based on reactants rate = -(D[N 2 O 5 ]/ D t Appearance is based on products rate = D[NO 2 ]/ D t rate = D[O 2 ]/ D t Converting rates of Appearance. rate = (D[NO 2 ]/ D t = - 4/2 D[N 2 O 5 ]/ D t D[O 2 ]/ D t = - 1/2 D[N 2 O 5 ]/ D t 13-9 13-10 1) What is the rate of a chemical reaction? (Describe in your own words and then in equation) a A ----> b B + c C 2) Answer the following Given the chemical reaction: a) What s the rate of disappearance ( or decomposition) N 2 O 5? (Equation) b) What are the rates of appearance of NO 2 and O 2? (Equations) 13-11 13-12 3
2) Answer the following Given the chemical reaction: c) What are the rates of reaction based on N 2 O 5, NO 2, and O 2? (Equations) 2) Answer the following Given the chemical reaction: e) Are the rate of reaction based on N 2 O 5, NO 2, and O 2 equal? (Equations and explanation) d) Are the rates of decomposition based on N2O5, and formation based on, NO 2, and O 2 equal? (Explanation) 13-13 13-14 2) Answer the following Given the chemical reaction: e) Are the rate of reaction based on N 2 O 5, NO 2, and O 2 equal? (Equations and explanation) 3) What are the differences between average and instantaneous reaction rates? Refer to graph in new concepts. 4) Why is instantaneous rates of N 2 O 5 and NO 2 are negative and positive respectively? 13-15 13-16 4
Graphing Kinetics Data 2 N 2 O 5 (g) -----> 4 NO 2 (g) + O 2 (g) Graph of 2 N 2 O 5 (g) ---> 4 NO 2 (g) + O 2 (g) Average rate = 13-17 13-18 3) What are the differences between average and instantaneous reaction rates? Refer to graph in new concepts. Graph 4) Why is instantaneous rates of N 2 O 5 and NO 2 are negative and positive respectively? 13-19 13-20 5
Graph in Problem 7 Time / min [N 2O 5 ] / moldm - 3 0 0.01756 20 0.00933 40 0.00531 60 0.00295 80 0.00167 100 0.00094 160 0.00014 0.02 0.015 0.01 0.005 0 0 50 100 150 200 5) At what time the reaction is complete? Series1 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 = 2.06 x 10-4 mol dm -3 min -1 20-40 = 40-60 = 60-80 = 13-21 13-22 7) How does reaction rate vary with time in the graph? Consider the decomposition of N 2 O 5. 8) What are the main factors that affect a rate of a chemical reaction? 13-23 13-24 6
Factors that affect rates of chemical reactions Effect of Particle Size on Rate a) Temperature b) Concentration c) Catalysts d) Particle size of solid reactants 13-25 13-26 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? 13-27 7