chm1011-tutorial-questions-week-12

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Studocu is not sponsored or endorsed by any college or university CHM1011 tutorial Questions Week 12 Chemistry I (Monash University) Studocu is not sponsored or endorsed by any college or university CHM1011 tutorial Questions Week 12 Chemistry I (Monash University) Downloaded by Timothy Handoko (hantimo210@gmail.com) lOMoARcPSD|23633319

CHM1011 Tutorial Week 12 Equations and Constants Zero Order reaction: [?] ? = [?] ? − ?? First Order reaction: [?] ? = [?] ? ???(−??) Second Order reaction (only one reactant A ): ? [?] ? − ? [?] ? = ?? Half-life: ? ?/? = ?.??? ? Tutorial Questions 1. Consider the reaction: Zn (s) + 2HCl (aq) → ZnCl 2 (aq) + H 2 (g) Explain why the reaction rate will increase when: a) you use powdered Zn instead of solid piece b) the temperature of the reaction is increased c) the concentration of HCl is doubled d) a catalyst is used. 2. The graph below shows the kinetics for the reaction x A + y B → z C . a) Determine the stoichiometry of this reaction (solve x , y & z ). 0.00 0.20 0.40 0.60 0.80 1.00 1.20 0 5 10 Concentration (M) Time (s) Kinetics Graph for the rxn xA + yB --> zC Concentration of A Concentration of C Concentration of B Downloaded by Timothy Handoko (hantimo210@gmail.com) lOMoARcPSD|23633319

b) Calculate the average rate for the depletion of A, from t = 5 s - t = 10 s. c) Calculate the instantaneous rate at t = 2 s for depletion of A. 3. Cyclopropane, C 3 H 6 , is a gas that is used as a general anaesthetic. It undergoes a slow rearrangement to propene. The tabulated data below was obtained for the conversion at 37 o C: a) What is the rate law for this reaction? b) What is the value of the rate constant, k (with correct units)? c) Calculate the half-life of cyclopropane 4. Hydrogen sulfide burns in oxygen to form sulfur dioxide and water: 2 H 2 S (g) + 3 O 2 (g) → 2 SO 2 (g) + 2 H 2 O (g) If SO 2 is being formed at a rate of 0.60 mol L -1 s -1 , what are the rates of consumption of H 2 S and O 2 ? 5. The reaction below has a rate law, Rate = k [A], with a rate constant, k = 2.12 × 10 -4 s -1 at 25°C. A + B → C a) What is the rate order for A and B? b) To the right, sketch the general shape of [A] verses time. Note: does not need to be to scale. c) The initial concentration of A is 0.35 M. What is [A] after 1 hour? Initial concentration of cyclopropane (mol L -1 ) Rate of formation of propene (mol L -1 s -1 ) 0.050 2.95 x 10 -5 0.100 5.90 x 10 -5 0.150 8.85 x 10 -5 → cyclopropane propene [A] time Downloaded by Timothy Handoko (hantimo210@gmail.com) lOMoARcPSD|23633319

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6. Ammonium cyanate (NH 4 NCO) rearranges in water to give urea (NH 2 ) 2 CO: NH 4 NCO (aq) → (NH 2 ) 2 CO (aq) The rate equation for this process is Rate = k [NH 4 NCO] 2 , where k = 0.0113 M -1 min -1 . If the original concentration of NH 4 NCO in solution is 0.229 M, how long will it take for the concentration to decrease to 0.180 M? Extension Questions 1. Below is a kinetic plot for reaction: xA + yB → zC a) determine the values of x, y and z for the stoichiometry of this reaction b) determine the rate of reaction between 20 seconds and 60 seconds c) determine the rate of reaction at 50 seconds Downloaded by Timothy Handoko (hantimo210@gmail.com) lOMoARcPSD|23633319

2. The plot on the right represents reaction rate verses concentration of molecule A. Circle the correct rate order for A: i) zero order ii) first order iii) second order Explain your reasoning: 3. The oxidation of iron (II) by cerium (IV): Ce 4+ + Fe 2+ → Ce 3+ + Fe 3+ is measured at several different initial concentrations of the two reactants: [Ce 4+ ] M [Fe 2+ ] M Rate (M sec -1 ) 1.1 x 10 -5 1.8 x 10 -5 2.0 x 10 -7 1.1 x 10 -5 2.8 x 10 -5 3.1 x 10 -7 3.4 x 10 -5 2.8 x 10 -5 9.5 x 10 -7 a) Write the rate expression for this reaction b) Determine rate order c) Calculate the rate constant k with correct units d) What is the overall rate order? e) Predict the initial rate of reaction when [Ce 4+ ] = 2.6 x 10 -5 M and [Fe 2+ ] is 1.3 x 10 -5 M 4. Predict how the rate of each reaction will be affected by doubling the concentration of the first species in each chemical equation: 2ICl + H 2 → I 2 + HCl Rate = k [ICl][H 2 ] _____________________ 2NO + O 2 → 2NO 2 Rate = k [NO] 2 [O 2 ] _____________________ OH - + (CH 3 ) 3 CBr → Br - + (CH 3 ) 3 COH Rate = k [(CH 3 ) 3 CBr] _______________ Reaction rate [A] Downloaded by Timothy Handoko (hantimo210@gmail.com) lOMoARcPSD|23633319

5. The following reaction has a rate constant k = 8.93 x 10 6 L mol -1 s -1 . 2H S S + 3O 2 → 2SO 2 + 2H 2 O a) What is the rate order? Explain your answer. b) If the concentration of O 2 decreased from 0.112 M to 0.053 M in first 3 minutes, calculate the average rate of change in [O 2 ]. 6. The dimerization of tetrafluoroethylene to octafluorocyclobutane is the following reaction: 2C 2 F 4 (g) → C 4 F 8 At 450 K the rate constant is k = 0.0448 M -1 s -1 . If the initial concentration of C 2 F 4 is 0.0100 M, what is the concentration after 5 minutes? Challenging Questions 1. What is the difference between the differential and integrated rate laws? When would you use one over another? 2. What factors change the value of the rate constant, k ? 3. How can you measure a reaction rate of a reaction where both the reactants and products are colourless? Downloaded by Timothy Handoko (hantimo210@gmail.com) lOMoARcPSD|23633319

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