CHEM 1212 1nd Edition Lecture 12 Outline of Last Lecture I Linear formats II Half Life III Collision Theory Outline of Current Lecture I Practice Problems II Chemical Equilibrium Current Lecture The ozone of the stratosphere can be decomposed by reaction with nitrogen dioxide commonly called nitric oxide from high flying jet aircraft O3 g NO g NO2 g O2 g The rate expression is rate k O3 NO Which of the following mechanisms is consistent with the observed rate expression A B A NO O3 NO3 O slow NO3 O NO2 O2 fast B NO O3 NO2 O2 slow one step C O3 O2 O slow O NO NO2 fast D NO N O slow O O3 2O2 fast O2 N NO2 fast Chapter 16 Chemical Equilibrium Equilibrium is based on understanding kinetics The Equilibrium State o Consider the reaction A B Ratef kf A Rater kr B o At equilibrium rate of the forward reaction the rate of the reverse reaction Kf kr B A o At equilibrium the reaction does not stop o In the kinetic region the system is approaching equilibrium Kf kr Kc o Equilibrium constant values do not have units Kc B A ratio of equilibrium concentration of the species The reaction below represents a single elementary step in equilibrium 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 2SO2 g O2 g 2SO3 g What is the rate law expression for the forward reaction Ratef kf SO2 2 O2 What is the rate law expression for the reverse reaction Rater kr SO3 2 What is the value of Kc Kc 15 o Kf 0 15s 1 o Kr 1 00s 1 Chemical equilibrium can be established wither from the forward or the reverse direction Reconsider this gaseous reaction o 2SO2 g O2 g 2SO3 P MRT o Kp PSO32 PSO22 x PO2 atm SO3 RT 2 SO2 RT 2 x O2 RT Kc x RT 1 Kp Kc RT n of moles of gaseous products of moles of gaseous reactants o Solids do not show up in equilibrium constant expressions Meaning of Kc o The numerical value of Kc distinguishes whether the reaction as written is product favored or reactant favored A B o What must be true for the value of Kc to be less than one Reactant favored Concentration of A must be greater than B o What must be true in order for Kc to be greater than one Product favored Concentration of B must be greater than A The reaction Quotient Q o 2SO2 g O2 g 2SO3 g o Q SO3 2 SO2 2 x O2 o Kc Q reaction favors production of reactants to reach equilibrium o Kc Q at equilibrium o Kc Q Reaction favors production of products to reach equilibrium ICE Tables and Kc o PCl5 g PCl3 g O2 g PCl5 Initial Concentration 1 0 M Change in 0 60 M Concentration Equilibrium 0 40 M Concentration PCl3 0 0 60 M O2 0 0 60 M 0 60 M 0 60 M