Lecture 8 Questions 1 and 2 2N 2 6H2O 1 For the oxidation of ammonia 4NH3 3O2 it was found that the rate of formation of N2 was 0 27 mol L 1 s 1 A At what rate was water being formed Ans H2O t 0 81 M s N2 0 27 6 H2O H2O B At what rate was ammonia being consumed Ans NH3 t disappearing at a rate of 0 54 M s 0 27 NH3 0 27 4 NH3 NH3 t disappearing at a rate of 0 54 M s 2 For the reaction A 2 B 3 C D What is the magnitude of the rate of change for B when C is increasing at 4 6 M s Answer 3 1 M s C t B t 4 6 3 1 For every 3C there are 2B Lecture 9 Questions 3 and 4 3 The reaction A 2B C Products has a rate law of Rate k A B a By what factor would the rate change if A is tripled Ans 9 3A 3 x A b What is the overall rate law Ans 3 or 3rd add exponents 2 1 3 c What rate order is A B and C Ans A 2 B 1 C 0 4 Using the information in the table Find a the rate law for the reaction Rate k B When you are trying to find the rate order for A keep B the same and see how A affected the rate Vice versa for B A had no effect on rate therefore zero order doesn t affect rate As B doubled Rate quadrupled in this chat therefore the rate order is 2 2 2 x b the value of the rate constant k 0 722 M min Use the formula representing rate Rate k B To solve for k plug in the values from any of the three rows 0 0234M min k 0 180M Double check units or the specific order c the rate when A is 1 5x10 3 and B is 1 5x10 3 Rate 0 00000162 M min Now we know Rate k B Plug 1 5x10 3 for B 0 722 for k remember that A doesn t matter in this question Lecture 10 Questions 5 and 6 5 What is the rate constant of a first order reaction when 20 0 of a reactant remains after 30 0 s Use first order rate formula and solve for the rate constant Make sure to set your initial concentration to x 100 and your final concentration to 2 or whatever percentage the problem give you for what remains 6 A substance decomposes with a rate constant of 9 05 10 s How long does it take for 15 0 of the substance to decompose Notice that you must use units to figure out what formula to use because it is s 1 we can assume first order For this wording set your initial concentration to 100 x and use the final concentration to be 1 15 or 85 remaining Solve for t Lecture 11 Questions 7 and 8 7 The activation energy Ea for a particular reaction is 37 8 kJ mol If the rate constant at 280 K is 0 178 M s then what is the value of the rate constant at 381 K R 8 314 J mol K 8 Determine the activation energy for the redox reaction Q 2 R Q 2 R Lecture 12 Questions 9 and 10 1a What is the molecularity of the rate determining step in the proposed mechanism Answer Termolecular 1b Are there intermediates If so identify the intermediate Answer Yes N2O is the intermediate 2 Consider the multistep reaction What is the best rate law for the overall reaction Answer Rate k A 2 B Lecture 13 Questions 11 and 12 11 The following reaction is at equilibrium in a closed 6L vessel N g 3H g 2NH g What will happen if the vessel volume is increased to 8L Assume constant temperature Ans In this case it would cause a shift to the left side and there would be an increase in N2 and 3H2 We know that as the volume increases the pressure will decrease Because of the decrease in pressure there will be a shift to the side with more moles We must only count the moles that deal with the gas state 12 For the reaction below the partial pressure of NO is 0 50 atm and the partial pressure of N O is 0 25 atm What must happen for the reaction to reach equilibrium 2 NO g N O g Kp 0 25 Ans The reaction needs to shift in the reverse direction To solve this we can start by solving for our Q and then compare that to our K value 25 5 2 1 Q Because our Q K we must shift the reaction towards the reverse or towards the reactants in order to lower Q reach our K equilibrium value Know how to compare Q and K Lecture 14 Questions 13 Ans When NH3 is removed the system shifts to the left Temp increased causes a shift to the left We can treat the delta H like a reactant Exothermic you treat it like a product and and endo you treat it like a reactant In this case it would be like a product and when we increase a product the rxn will shift to the right Volume decreased causes no shift There is no gases so a chance in volume does nothing HCl causes the reaction to shift to the left NH4Cl being added causes a shift to the left Remember NH4Cl will dissociate into 2 ions those ions being NH4 After the dissociation there will be more NH4 in the system causing a shift to the and Cl left to rebalance equilibrium Lecture 15 Questions 14 and 15 1 An empty steel container is filled with 2 0 atm of H and 1 0 atm of F The system is allowed to reach equilibrium according to the reaction below If Kp 0 45 for this reaction what is the equilibrium partial pressure of HF H g F g 2 HF g Answer 0 70 atm 2 If Kc 0 0084 for the reaction below at 298 K then what is the value of Kp 3 A g B g C g D g Answer 1 4 x 10 5
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