CHEM 135 1st Edition Exam 2 Study Guide Lectures 10 17 Lecture 10 February 16 Rate vs reaction concentration When placed in a graph format Zero order reaction has a straight horizontal line First order reaction has a straight increasing slope Second order reaction has an arched increasing slope Complex rate law and reaction order aA bB cC dD Rate k A m B n k rate constant m n reaction order with respect to A B Overall reaction order m n Ex Determining the order and rate constant of a reactionConsider the reaction between nitrogen dioxide and carbon monoxide NO2 M 0 10 0 20 0 20 0 40 NO2 g CO g NO g CO2 g CO M 0 10 0 10 0 20 0 10 Initial Rate M s 0 0021 0 0082 0 0083 0 033 The initial rate of the reaction is measured at several different concentrations of the reactants with accompanied results From the data determine a The rate law for the reaction b The rate constant k for the reaction Answers to this example are on p 607 Lecture 11 February 18 Integrated Rate Law Zero order graph A on y axis and time on x axis slope k First order graph ln A on y axis and time on x axis slope k Second order graph 1 A on y axis and time on x axis slope k Equations Zero order A kt A initial First order ln A kt ln A initial Second order 1 A kt 1 A initial Half Life Time it takes for the concentration of the reactant to fall to one half its original value Zero order reaction t1 2 Ainitial 2k First order reaction t1 2 0 693 k Second order reaction t1 2 1 k A0 Ex Determining the concentration of a reactant at a given time The decomposition of SO2Cl2 is first order and has a rate constant of 2 90 x 10 4s 1 If the reaction is carried out at the same temperature and the initial concentration of SO 2Cl2 is 0 0225M what will the SO2Cl2 concentration be after 865s Answer on p 610 Ex Half life Molecular iodine dissociates at 625K with a first order rate constant of 0 271 s 1 What is the half life of this reaction Answer on p 611 Ex This reaction was monitored as a function of time A B C A plot of ln A versus time yields a straight line with a slope of 0 0045 s a b c d What is the value of the rate constant k for this reaction at this temperature Write the rate law for the reaction What is the half life If the initial concentration of A is 0 250M what is the concentration after 225s Answer on p A 16 Ex The decomposition of SO2Cl2 is first order in SO2Cl2 and has a rate constant of 1 42 x 10 4s 1 at a certain temperature a What is the half life for this reaction b How long will it take for the concentration of SO2Cl2 to decrease to 25 of its initial concentration c If the initial concentration of SO2Cl2 is 1 00M how long will it take for the concentration to decrease to 0 78M d If the initial concentration of SO2Cl2 is 0 150M what is the concentration of SO2Cl2 after 2 00 x 102s Answer on p A 16 Lecture 12 February 20 Factors affecting the rate of a reaction 1 Concentration If there is an increase in the concentration there is an increase in the frequency of collisions 2 Temperature If there is an increase in temperature the frequency of collisions also increase 3 Surface area Among the colliding molecules only effective collisions i e collisions in right orientation and with right energy can lead to product formation Frequent collisions raise the rate of the reaction Collisions need sufficient energy to break reactant bonds Lecture 13 February 23 Activation energy in a chemical reaction Ea Lower the activation energy faster the rate of reaction REMEMBER frequent collisions energetic collision correct orientation product Arrhenius equation Takes into account all factors that affect the rate of a reaction k Ae E a RT k rate constant Ae Arrhenius factor collision frequency and orientation factor R gas constant T temperature in kelvin Ea energy barrier to be surmounted in going from reactants to products ln The Arrhenius equation has two derivatives Ea 1 ln k ln A R T k2 E a 1 1 k1 R T 1 T 2 Reaction Mechanism and Reaction Intermediate Unimolecular A product rate k A 1 Bimolecular 2A product rate k A 2 Termolecular A B product rate k A B 1 3A product rate k A 3 A B C product rate k A B 1 C 1 Reaction intermediates appear in the elementary steps but not in the final balanced overall reaction Rate Determining Step Rate determining step slow step determines the rate law of the overall reaction Rate law of slow step rate law of overall reaction Ex Using the two point form of the Arrhenius equation Consider the reaction between nitrogen dioxide and carbon monoxide NO2 g CO g NO g CO2 g The rate constant at 701K is measured as 2 57M 1 s 1 and that at 895K is measured as 567M 1 s 1 Find the activation energy for the reaction in kJ mol Answer on p 620 Ex The activation energy of a reaction is 56 8 kJ mol and the frequency factor is 1 5 x 10 11 s Calculate the rate constant of the reaction at 25 C Answer on p A 16 Ex The rate constant k for a reaction was measured as a function of temperature A plot of ln k versus 1 T in K is linear and has a slope of 7445K Calculate the activation energy for the reaction Answer on p A 16 Lecture 14 February 25 REVIEW DAY FOR CHAPTER 13 For extra practice on Chapter 13 P 638 25 29 31 35 35 odds 45 49 51 57 59 61 65 69 73 Lecture 15 February 27 Chemical Equilibrium N2 3H2 2NH3 This equation can go both ways and is reversible The rates of the reaction are the same meaning they are at equilibrium no significant change in concentration Does this mean the reaction stops No there is constant movement even in equilibrium in order to keep the reaction balanced Reversible Reactions and Equilibrium Constants aA bB cC dD Rates of the forward and reverse reactions are equal at equilibrium Equilibrium does NOT mean the products are equal K eq products reactants K eq C c D d A a B b The constant within this equation is unitless If Keq 1 it consists of more product than reactant greater numerator If Keq 1 it consist of more reactant than product greater denominator Heterogeneous Equilibrium Reactants and products are in different phases o 2CO2 g CO2 g C s CO C O2 2 o Equilibrium constant 2 KC Do not include pure solids and pure liquids in an equilibrium …