== Ch. 6 Review == 

 Understanding Concepts 
 1. pressure or volume, conductivity, absorbency of light 
 2. concentration, temperature, catalysis, chemical nature of reactants 
 3. Additional surface area = 18 � 1 cm2 
 Total surface area = 24 cm2 
 Proportional change in surface area = � 
 26/4cm2� = 4 
 The rate would be multiplied by a factor proportional to the surface area change: 
 r = 4 � 20 mL/s 
 r = 80 mL/s 
 4. (a) rate increases 
 (b) rate decreases 
 (c) rate increases 
 (d) rate increases 
 5. (a) r = � 
 r = 1.47 mL/s 
 (b) (i) With a 5ºC increase in temperature, the rate could be doubled and the time halved. 
 (ii) Without the catalyst, the reaction might be imperceptibly slow. 
 6. (a) r = k [ClO2(aq)]2[OH– 
 (aq)] 
 (b) This is a third-order reaction. 
 (c) The rate would quadruple. 
 (d) The rate would double. 
 7. (a) When we compare Trials 1 and 2, we see that as [Cl2] is doubled, rate is multiplied by 2; therefore, rate depends 
 on [Cl2]1. 
 When we compare Trials 2 and 3, we see that as [NO] is doubled, rate is multiplied by 4; therefore, rate depends 
 on [NO]2. 
 Overall, r = k [Cl2]1[NO]2. 
 (b) The rate-determining step is most likely to be 
 2 NO(g) + Cl2(g) → product or intermediate 
 (c) k = � 
 [NO]2 
 r 
 [Cl2] 
 � 
 = 
 k = 18 L2/(mol2• s) 
 (d) r = k [NO]2 [Cl2] 
 = 18 L2/(mol2• s) (0.30 mol/L)2 � 0.40 mol/L 
 r = 0.65 mol/(L• s) 
 1.8 � 10�2 mol/(L•s) 
 ��� 
 (0.10 mol/L)2 � 0.10 mol/L 

 8. (a) Half-life is the amount of time for one-half the mass of a radioisotope to decay. 
 (b) 14.0 a is four half-lives. The percentage remaining is 100% � (� 
 1 
 �)4 = 6.25%. 
 11. (a) There are generally one, two, or three particles involved in each elementary step. 
 (b) Collisions of more particles at the same point in time and space are much less probable as the number of particles 
 increases. Four-body collisions are effectively impossible as contributors to a reaction process. 
 12. (a) A catalyst might be consumed in one step of a mechanism as long as it is regenerated in a subsequent step. 
 (b) Homogeneous catalysts, like acid in aqueous solution, are in the same phase as reactants. Heterogeneous catalysts, 
 like platinum in gases, are in different phases from reactants. 
 13. (a) catalyst (necessary in first step but regenerated): Cu2+ 
 (aq) 
 intermediates (produced but then consumed): Cu+ 
 (aq), I(aq), CuSO4 
 + 
 (aq) 
 (b) S2O8 
 2– 
 (aq) + 2 I– 
 (aq) → I2(aq) + 2 SO4 
 2– 
 (aq) 
 (c) Since the I– 
 (aq) is not part of the rate-determining (slow) step, increasing its concentration will have no effect on 
 the overall rate. 
 (d) Since the S2O8 
 2– 
 (aq) is part of the rate-determining (slow) step, increasing its concentration will increase the overall 
 rate. 

 15. (a) When we compare Trials 1 and 2, we see that as [W] is doubled, rate is unchanged; therefore, rate depends on [W]0. 
 When we compare Trials 1 and 3, we see that as [X] is doubled, rate is multiplied by 2; therefore, rate depends 
 on [X]1. 
 When we compare Trials 1 and 4, we see that as [Y] is doubled, rate is multiplied by 4; therefore, rate depends 
 on [Y]2. 
 Overall, r = k [X]1 [Y]2. 
 (b) The rate-determining step is X + 2Y → products. 
 (c) A possible mechanism might be: 
 X + 2Y → XY2 (slow) 
 XY2 + W → WXY2 (fast) 
 WXY2 + X → Z (fast) 

 16. (a) When we compare Trials 1 and 2, we see that as [Hbn] is doubled, rate is multiplied by 2; therefore, rate depends 
 on [Hbn]1. 
 When we compare Trials 2 and 3, we see that as [CO] is tripled, rate is multiplied by 3; therefore, rate depends 
 on [CO]1. 
 (b) The overall order is two. 
 (c) Overall, r = k [Hbn]1 [CO]1. 
 (d) The carbon monoxide rate constant might be expected to be larger than the oxygen rate constant because it seems to 
 bind so quickly to hemoglobin. On the other hand, as will be discovered in the next unit, the more significant factor 
 is the equilibrium constant for the binding reaction, which is much larger for carbon monoxide than for oxygen.