CHEM 1212 1st Edition Lecture 13 Outline of Last Lecture Practice Problems Chemical Equilibrium Outline of Current Lecture Practice Problems Quadratic Equation Avoiding the Quadratic Equation Current Lecture H2 g I2 g 2HI g The equilibrium constant for the reaction above is 49 at 450 degrees C 0 22 mole of I 2 0 22 mole of H2 and 0 66 mole of HI were put into an evacuated 1 00 L container a The system is at equilibrium b Reactants needs to be made to get to equilibrium c Products needs to be made to get to equilibrium What is the rate expression that corresponds to the reaction mechanism given o A B C fast equilibrium Ratef kf A B rater kr C Kf A B kr C C kf kr A B o C D E slow Rate k C D Rate k kc A B D A researcher places 1 5 atms of nitrogen dioxide in a flask at 25 degrees C The researcher then monitors the total pressure of the flask over time as the nitrogen dioxide is allowed to react to produce dinitrogen tetroxide and reach equilibrium Given the researchers data what is Kc for this reaction o 2NO2 g N2O4 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 Time min 0 5 10 15 20 25 30 Total P atm 1 500 1 349 1 198 1 047 896 896 896 pN2O4 0 604 pNO2 0 292 Answer Kp 7 08 Kc 173 Quadratic Equation o A B 2C o If one mole of A and 2 moles of B are placed into a 1L flask and allowed to react what are the concentrations of A B and C at equilibrium o Answer Kc 2x 2 1 x 2 x plug into quadratic equation find x and plug in to find the final concentrations of A B and C Avoiding the Quadratic Equation o Same problem as above o Kc 2x 2 1 x 1 x 2x 2 1 x 2 o Take square root of both sides the square root of Kc 2x 1 x The reaction N2 g O2 g 2NO g o Contributes to air pollution whenever a fuel is burned in air at a high temperature as in a gasoline engine At 1500K K 1 0x10 5 Suppose a sample of air has N2 0 80 mol L and O2 0 20 mol L before any reaction occurs Calculate the equilibrium concentrations of reactants and products after the mixture has been heated to 1500K Write Kc equation Build ICE chart Put expressions in the equilibrium constant equation Kc 1 0x10 5 Assume x is much less than 2 which gets rid of the x s on the bottom of the equation only make assumptions when x is being subtracted or added Check to make sure assumption is right X 6 3x10 4