CHEM 0120 1st Edition Lecture 5 Outline of Current Lecture I Expressing Rates of Reactions II Integrated Rate Laws III Example 13 5 IV Half Life V Elementary Reactions Current Lecture I Expressing rates of reactions aA bB cC dD Rate 1 A a t 1 B 1 C 1 D b t c t d t Rates are expressed as positive quantities Example Chapter 13 44 What is the average rate of reaction in this time interval 2FeCl3 SnCl2 2FeCl2 SnCl4 redox reaction Fe3 Fe2 Fe3 I 0 03586M 4 minutes Fe3 f 0 02715M FeCl 3 t 0 02715 0 03586 M 4 minutes 0 00871 4 minutes 0 00218 II mol L second Integrated Rate Laws relate concentration or change in concentration to time and also provide an alternative method for determining rate of reaction A First Order 2N2O5 g 2NO2 g 02 g These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Rate k N2O5 Rate N 2 O5 t General ln k N2O5 A t kt A o Applied ln N 2 O5 t N 2 O 5 t kt N 2O 5 o Linear ln A t ln A o kt y b mx Slope rate constant k Slope rate constant k Slope rate constant k straight line first order B Second Order 1 1 kt A t A o y b mx C Zero Order A t A o kt y III b mx Example 13 5 Using Integrated Rate Law 2N2O5 g 4NO2 g O2 g first order reaction N2O5 o 1 65 x 10 2 M N2O5 t unknown k 4 80 x 10 4 t 6 00 x 102 s ln N2O5 t ln N2O5 o kt ln N2O5 t ln 1 65 x 10 2 M 4 80 x 10 4 6 00 x 102 s ln N2O5 t 4 393 N2O5 t e 4 393 N2O5 t 0 0123 M IV Half Lives t time it takes for a reactant to decrease to of its initial value A First order reaction A t A o ln At kt Ao A 1 2 o A o kt ln ln 12 kt 0 693 kt 1 2 0 693 kt 1 2 0 693 t 1 2 k B Second Order Reaction 1 1 t 2 k A t Half life increases C Zero Order Reaction A 2k V t 1 2 Rate is slower Elementary Reactions a single molecular event when determining m n we use initial rate method integrated rate method but not stoichiometric unless it is an elementary reaction because then the one step is the rate determining step Unimolecular reaction Rate k A Bimolecular Reaction Rate k A 2 Termolecular Reaction Rate k A 3