13-1 CHEM 102, Fall 2013, LA TECH Instructor: Dr. Upali Siriwardane Office: CTH 311 Phone Office Hours: M,W 8:00-9:30 & 11:00-12:30 am; Tu,Th, F 8: :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 :00-11:15 am., CTH 328

13-2 CHEM 102, Fall 2013, LA TECH Chapter 13. Chemical Kinetics 13.1 Catching Lizards The Rate of a Chemical Reaction The Rate Law: The Effect of Concentration on Reaction Rate The Integrated Rate Law: The Dependence of Concentration on Time The Effect of Temperature on Reaction Rate Reaction Mechanisms Catalysis 593

13-3 CHEM 102, Fall 2013, 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)

13-4 CHEM 102, Fall 2013, LA TECH How do you measure rates? How do you measure rates? Rates are related to the time it required to decay Rates are related to the time it required to decay reactants or form products. The rate reaction = change in concentration of The rate reaction = change in concentration of reactants/products per unit time Average rate Average rate rate of reaction = –  [reactant]/  t Instantaneous rate Instantaneous rate rate of reaction = – d[reactant]/dt H 2 + I 2 --> 2 HI

13-5 CHEM 102, Fall 2013, LA TECH Reaction of cis-platin with Water Substitution reaction

13-6 CHEM 102, Fall 2013, LA TECH Disappearance of Color Intensity of Color is proportional to amount of reactant

13-7 CHEM 102, Fall 2013, LA TECH

13-8 CHEM 102, Fall 2013, LA TECH 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 = -(  [N 2 O 5 ]/  t Appearance is based on products rate =  [NO 2 ]/  t rate =  [O 2 ]/  t Converting rates of Appearance and disapperence. rate = (  [NO 2 ]/  t = - 4/2  [N 2 O 5 ]/  t  [O 2 ]/  t = - 1/2  [N 2 O 5 ]/  t

13-9 CHEM 102, Fall 2013, LA TECH Measuring Reaction Rate a A --> b B Based on reactants rate = -(1/a)  [A]/  t Based on products rate = +(1/b)  [B]/  t  [A]= [A] f - [A] I Change in A  t= t f - t i Change in t

13-10 CHEM 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 a A ----> b B + c C

13-11 CHEM 102, Fall 2013, LA TECH 2) Answer the following Given the chemical reaction: 2 N 2 O > 4 NO 2 + O 2 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)

13-12 CHEM 102, Fall 2013, LA TECH 2) Answer the following Given the chemical reaction: 2 N 2 O > 4 NO 2 + O 2 c) What are the rates of reaction based on N 2 O 5, NO 2, and O 2 ? (Equations) d) Are the rates of decomposition based on N 2 O 5, and formation based on, NO 2, and O 2 equal? (Explanation)

13-13 CHEM 102, Fall 2013, LA TECH 2) Answer the following Given the chemical reaction: 2 N 2 O > 4 NO 2 + O 2 e) Are the rate of reaction based on N 2 O 5, NO 2, and O 2 equal? (Equations and explanation)

13-14 CHEM 102, Fall 2013, LA TECH 2) Answer the following Given the chemical reaction: 2 N 2 O > 4 NO 2 + O 2 e) Are the rate of reaction based on N 2 O 5, NO 2, and O 2 equal? (Equations and explanation)

13-15 CHEM 102, Fall 2013, 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 N 2 O 5 and NO 2 are negative and positive respectively?

13-16 CHEM 102, Fall 2013, LA TECH 3) What are the differences between average and instantaneous reaction rates? Refer to graph in new concepts.

13-17 CHEM 102, Fall 2013, LA TECH 4) Why is instantaneous rates of N 2 O 5 and NO 2 are negative and positive respectively?

13-18 CHEM 102, Fall 2013, LA TECH 2 N 2 O 5 (g) -----> 4 NO 2 (g) + O 2 ( g) Graphing Kinetics Data Average rate =

13-19 CHEM 102, Fall 2013, LA TECH Graph

13-20 CHEM 102, Fall 2013, LA TECH Graph in Problem 7 Time / min [N 2 O 5 ] / moldm ) At what time the reaction is complete?

13-21 CHEM 102, Fall 2013, 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 [N 2 O 5 ] f - [N 2 O 5 ] i = 2.06 x mol dm -3 min -1 t f - t i 0-20 = - ½ [ ] - [ ] = 2.06 x mol dm -3 min = = =

13-22 CHEM 102, Fall 2013, LA TECH 7) How does reaction rate vary with time in the graph? Consider the decomposition of N 2 O 5.

13-23 CHEM 102, Fall 2013, LA TECH a) Temperature b) Concentration c) Catalysts d) Particle size of solid reactants Factors that affect rates of a chemical reactions

13-24 CHEM 102, Fall 2013, LA TECH 8)What are the main factors that affect a rate of a chemical reaction?

13-25 CHEM 102, Fall 2013, LA TECH Effect of Particle Size on Rate

13-26 CHEM 102, Fall 2013, 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?