Spring 2014 Chemistry II Chapter 13

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1 CHAPTER 13 - Chemical Kinetics: Rates of Reactions 01-[13z]. Review the data below for the catalytic cracking of cyclohexane at 500 C. What is the order of the reaction? Concentration of Cyclohexane, M Time, sec (A) one-half order. (D) zero order. 02-[13z]. What is the half-life, in years, of a pesticide malathion if it is found that 95% of it disappears after 10 years? (A) 0.83 (B) 5.0 (C) 10.0 (D) 1.2 (E) 0.43 (F) 2.3 (G) [13z]. The gas-phase reaction, Cl(g) + HBr(g) HCl(g) + Br(g), has an overall enthalpy change of -66 kj. The activation energy for the reaction is 7 kj. What is the activation energy (in kj) of the reverse reaction? (A) 66 (B) 7 (C) 73 (D) 59 (E) zero (F) cannot be determined 04-[13z]. A catalyst functions by: (A) decreasing the ΔH of the reaction. (B) increasing the ΔH of the reaction. (C) decreasing the E a of the reaction. (D) increasing the E a of the reaction. (E) converting the reaction from endothermic to exothermic. 05-[13z]. A catalyst cannot: (A) change the mechanism of a reaction. (B) change the rate of a reaction. (C) change the ΔH of a reaction. (D) change the E a of a reaction. 06-[13z]. What element is the best catalyst for the Haber process, for a catalytic converter, and for catalytic hydrogenation? (A) rubidium (B) platinum (C) calcium (D) copper (E) lithium 07-[13z]. The rate constant k of a reaction will generally change, as we change all of the following variables except one. Which is it? (A) change the concentrations of the reactants (B) change the activation energy (C) change the temperature (D) change the catalyst

2 08-[13z]. Review the data below for the reaction X + Y Z. Initial conc. of X Initial conc. of Y Initial rate For X, the reaction must be: (A) first order. (B) second order. (C) zero order. 09-[13z]. Review the data below for the reaction X + Y Z. Initial conc. of X Initial conc. of Y Initial rate For Y, the reaction must be: (A) first order. (B) second order. (C) zero order. 10-[13z]. Consider the following reaction: 2Al + 3Br 2 2AlBr 3. Once we have balanced the equation, we then know that the order of this reaction with respect to aluminum: (A) must be zero order. (B) must be first order. (C) must be second order. (D) cannot be known until laboratory experiments are conducted. 11-[13z]. Review the data below for the reaction X + Y Z. Initial conc. of X Initial conc. of Y Initial rate For X, the reaction must be: 12-[13z]. Review the data below for the reaction X + Y Z. Initial conc. of X Initial conc. of Y Initial rate For Y, the reaction must be: 13-[13z]. Review the data below for the biochemical decomposition of tryptophane in the blood at 37 C. Conc. of tryptophan, ppm Time, sec What is the order of the reaction? (A) zero order (B) one-half order (C) first order

3 (D) second order. 14-[13z]. Predict an element in the second row of transition metals of the periodic table (i.e., the row starting with rubidium) that would serve as a good catalyst for catalytic hydrogenation. (A) Zr (B) Nb (C) Mo (D) Pd (E) Ag (F) Cd 15-[13z]. The two types of catalysts are: (A) heterogeneous and homogeneous. (B) first order and second order. (C) primary and secondary. 16-[13z]. Increasing the activation energy of a reaction will: (A) slow down the reaction. (B) speed up the reaction. (C) have no effect on the rate of the reaction. 17-[13z]. The rate constant k of a reaction changes as the temperature of the reaction varies. 18-[13z]. The activation energy of a reaction changes as the temperature of the reaction varies. 19-[13z]. Consider the reaction X Z, where the rate is observed as Rate = k[x] 1/2, that is, the reaction is one-half order. Which plot below would be linear? (A) [X] vs time with the slope = k (B) ln(x) vs time with slope = k (C) ln(rate) vs ln(x) with the slope = 1 2 (D) 1/(Rate) vs 1/[X] with the slope = k 20-[13z]. Which is not true about an enzyme? (A) It is a protein. (B) It is a catalyst. (C) It occurs in both plants and animals. (D) It makes a reaction go by changing it from endothermic to exothermic. 21-[13z]. The rate of a reaction can typically be increased by increasing the concentrations of the reactants. 22-[13z]. The rate constant of a reaction can typically be increased by increasing the concentrations of the reactants. 23-[13z]. The rate of a reaction can typically be increased by increasing the E a of the reaction. 24-[13z]. The rate of a reaction can typically be increased by increasing the surface area of a solid reactant or catalyst. 25-[13z]. The rate of a reaction can typically be increased by increasing the ΔH of the reaction.

4 26-[13z]. The rate of a reaction can typically be increased by increasing the temperature. 27-[13z]. An automobile catalytic converter converts carbon monoxide to carbon dioxide. 28-[13z]. An automobile catalytic converter converts unburned fuel to carbon dioxide and water. 29-[13z]. An automobile catalytic converter converts water to hydrogen and oxygen. 30-[13z]. An automobile catalytic converter converts nitrogen oxides to nitrogen and oxygen. 31-[13z]. For the reaction A B, a plot of the reciprocal of [A] vs time is linear. The reaction is: (D) need more data to determine. 32-[13z]. For the reaction A B, a plot of the logarithm of [A] vs time is linear. The reaction is: (D) need more data to determine. 33-[13z]. For the reaction A B, a plot of [A] vs time is linear. The reaction is: (D) need more data to determine. 34-[13z]. What is the half-life, in years, of the pesticide DDT if it is found that 80% of DDT remains after 5 years (20 C, Lake Wishiwanqua)? (A) 5.0 (B) 8.9 (C) 10.2 (D) 15.5 (E) 18.9 (F) [13z]. It is found that 500 mg of chymopopsin spontaneously decomposes in a first-order reaction to give 335 mg of chymopopsin in 2000 sec. Calculate the rate constant k (in sec -1 ). (A) 1.0 x 10-3 (B) 2.0 x 10-3 (C) 4.0 x 10-3 (D) 8.0 x 10-3 (E) 1.0 x 10-4 (F) 2.0 x 10-4

5 36-[13z]. To determine the activation energy of a reaction, you could: (A) plot ln[a] 0 vs ln [A] t. (B) determine k at various temperatures and plot ln(k) vs the reciprocal of the temperature. (C) plot the half-life of the reaction vs the reciprocal of the concentration. (D) multiply the order of the reaction by the concentration of the reactants. (E) plot concentration vs temperature. 37-[13z]. If you increase the temperature of a reaction from 50 C to 75 C, it is likely that the rate constant k will: (A) double. (B) halve. (C) increase by a factor of about 10. (D) increase by a factor of about (E) stay the same. 38-[13z]. Look below for data for the decomposition of aqueous hydrogen peroxide 2H 2 O 2H 2 2O + O 2, at 20 C. What is the order of the reaction? Time, min [H 2 O 2 ] (A) cannot be determined (B) varies upon the temperature (C) zero (D) first (E) second 39-[13z]. Look below for data for the reaction of 2A + B C + D. What is the rate expression? Initial Concentration [A] [B] Initial rate (mol/l-s) (A) Rate = [A] 2 [B] (B) Rate = k[a][b] (C) Rate = k[b] 2 (D) Rate = k[a] (E) Rate = k[a][b] x x x x [13z]. The decomposition of NOBr is second order, with a rate constant k = 25 L/mol-s at 20 C. If the initial concentration of NOBr is M, find the time (in sec) at which the concentration will be M. (A) 25 (B) 15.6 (C) 67 (D) 37 (E) [13z]. Popcorn kernels pop according to a first-order rate whereby 6 kernels pop in 5 seconds when 150 kernels are present. What is the half-life of the kernels, that is, how many seconds will it take for 75 kernels to pop, starting with 150? (A) 85 (B) 80 (C) 75

6 (D) 70 (E) [13z]. The rate constant for the decomposition of polystyrene trash in a dump is first order and is k = 0.7 yr -1. How long will it take (in years) for a 100 g sample to decompose to 1 g? (A) 2.8 (B) 6.6 (C) 12 (D) 44 (E) [13z]. Consider the enzyme insulin, which catalyzes the reversible reaction sugar starch. What is the purpose of this enzyme? (A) decrease ΔH for the reaction (B) increase the temperature (C) increase both k (forward rate constant) and k f r (reverse rate constant) for the reaction (D) increase E a for the reverse reaction (E) increase E a for the forward reaction (F) change K eq for the reaction. 44-[13z]. Consider the catalytic converter on an automobile, which converts pollutants to harmless compounds. Which is correct? (A) The catalyst makes the reaction faster by decreasing the quantity of heat ΔH evolved. (B) An ideal catalytic converter experiences a rapid destruction of platinum during the reaction. (C) The purpose of the catalyst is to convert N 2 to nitrogen oxides. (D) The catalyst makes the reaction faster by increasing the rate constant k. (E) The purpose of the catalytic converter is to convert carbon monoxide into octane. 45-[13z]. The decomposition of ozone O 3 (O 3 O 2) shows that a plot of ln[o 3 ] vs time is linear. We can conclude that the reaction: (A) may be second order. (B) must be second order. (C) may be zero order. (D) may be zero order. (E) must be first order. 46-[13z]. Which is not affected by a change of E a of a reaction? (A) rate of reaction (B) the exponential term of the Arhennius equation (C) rate constant k of the reaction (D) mechanism of the reaction (E) ΔH of a reaction 47-[13z]. The decomposition of ethyl iodide is a first-order processes where the rate constant k = 5.0x10-3 s -1. What is the half life of the reaction? (A) 139 sec (B) 2.5 x 10 3 sec (C) 500 sec (D) 342 sec (E) 49 sec 48-[13z]. The rate expression, Rate = k (with no expression of the concentration of the reactant), applies for: (A) gas reactions only. (B) second order reactions. (C) first order reactions. (D) zero order reactions. (E) only reactions expressed in minutes. 49-[13z]. After two half-lives (of a first-order reaction), where we started with 100 grams, how much material will be left?

7 (A) 99 grams (B) 50 grams (C) 75 grams (D) 67 grams (E) 25 grams 50-[13z]. The radioactive decay of uranium-238 is: (A) a zero-order process. (B) a second-order process. (C) a process that occurs more rapidly at low temperatures. (D) a bimolecular process. (E) a first-order process. 51-[13z]. A reaction which may occur in air polluted with nitrogen oxide is 2 NO(g) + O 2 (g) 2 NO(g) The following data is found: Expt 1 Initial Conc. [NO] Initial Conc. [O 2 ] Rate of Reaction Which is correct? The reaction is: (A) 1st order in [NO] and 1st order in [O 2 ]. (B) 2nd order in [NO] and 1st order in [O 2 ]. (C) 1st order in [NO] and 2nd order in [O 2 ]. (D) 2nd order in [NO] and 2nd order in [O 2 ]. (E) 0 order in [NO] and 2nd order in [O 2 ]. (F) 2nd order in [NO] and 0 order in [O 2 ]. 52-[13z]. For the following reaction at 1000 C, CO + 1 2O 2 CO x x x x x10-5 Expt 1 Initial Conc. [NO] Initial Conc. [O 2 ] Rate of Reaction x x x x10-5 Which is correct? The reaction is: (A) 1st order in [CO] and 1st order in [O 2 ]. (B) 2nd order in [CO] and 1st order in [O 2 ]. (C) 1st order in [CO] and 2nd order in [O 2 ]. (D) 2nd order in [CO] and 2nd order in [O 2 ]. (E) 0 order in [CO] and 2nd order in [O 2 ]. (F) 2nd order in [CO] and 0 order in [O 2 ]. 53-[13z]. Calculate the age of a piece of wood whose carbon-14 count is 35/min, compared with a fresh piece of wood the same size whose count is 125/min. (The half-life of C-14 is 5715 years). Give the answer in years. (A) 5700 (B) (C) (D) 1600 (E) [13z]. The decomposition of HI(g) to give H 2 (g) and I 2 (g) is 2nd order with a rate constant k equal to 30 M -1 min -1 at 443 C. How long does it take for a concentration of M of HI (g) to drop to half its value at 443 C? (A) 3.33 min (B) 1.57 min (C) 30 min

8 (D) 900 min (E) 9.00 min (F) 230 min 55-[13z]. The decomposition of N 2 O 5 (to give NO 2 and O 2) is a first-order processes where the rate constant k = 5.0x10-4 s -1. What is the half-life of the reaction? (A) sec (B) 2.5 x 10-4 sec (C) 1400 sec (D) 2500 sec (E) 840 sec (F) 11.2 sec (G) 4600 sec (H) 50,000 sec 56-[13z]. The decomposition of N 2 O 5 in the gas phase is described by 2 N 2O 5 (g) 4 NO(g) + O 2 (g). If a plot of 1/[N 2 O 5 ] vs time is not linear, then what can we conclude? The reaction (with respect to [N 2 O 5 ]): (A) must be 1st order. (B) may be 1st order. (C) cannot be 1st order. (D) may be 2nd order. (E) cannot be zero order. (F) must be 2nd order. 57-[13z]. The transformation of cyclopropane to propene is a first-order reaction with a rate constant of 5.4x10-2 /hr. How many hours must elapse for an initial concentration of M to drop to M? (A) hr (B) 0.54 hr (C) 5.4 hr (D) 13 hr (E) 18.5 hr (F) 185 hr 58-[13z]. Which is correct? (A) If a reaction is exothermic, a catalyst affects the quantity of heat evolved. (B) Nickel can be used as a catalyst for hydrogenation. (C) A catalyst for an equilibrium never changes k f (the rate constant of the forward reaction). (D) A catalyst can change the value of K eq (an equilibrium constant). (E) An ideal catalyst is destroyed during a reaction. 59-[13z]. Which is not correct? (A) If a reaction is endothermic, a catalyst can possibly change the reaction to exothermic. (B) Nickel can be used as a catalyst for hydrogenation. (C) A catalyst for an equilibrium can changes k f (the rate constant of the forward reaction). (D) A catalyst does not change the value of K eq (an equilibrium constant). (E) An enzyme is a catalyst. 60-[13z]. same as #54 61-[13z]. The decomposition of HI(g) to give H 2 (g ) and I 2 (g) is 2nd order with a rate constant k equal to 30 M -1 min -1 at 443 C. How long does it take for a concentration of 2.0 M of HI (g) to drop to one-tenth of its original value? (A) 3.3 min (B) 9 sec (C) 18 sec (D) 1.00 min (E) 45 sec (F) 2.3 min

9 62-[13z]. Assuming all other factors are the same, which of the following reactions would be the fastest (all energy unitsareinkj/mol)? (A) E a = 45, ΔH = -25 (B) E a = 35, ΔH = -10 (C) E a = 55, ΔH = -25 (D) E a = 60, ΔH = +5 (E) E a = 75, ΔH = [13z]. In catalytic hydrogenation, the role of the catalytic surface is to: (A) break the H 2 bond. (B) break the carbon-carbon p-bond. (C) increase the kinetic energy of H 2. (D) decrease the ΔH of the reaction. (E) form a hydrogen-hydrogen double bond.

CHEM Chapter 14. Chemical Kinetics (Homework) Ky40

CHEM Chapter 14. Chemical Kinetics (Homework) Ky40 CHEM 1412. Chapter 14. Chemical Kinetics (Homework) Ky40 1. Chlorine dioxide reacts in basic water to form chlorite and chlorate according to the following chemical equation: 2ClO 2 (aq) + 2OH (aq) ClO