Chapter11 - Chapter 11 Reaction Pathways Solutions for...

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Chapter 11 Reaction Pathways Solutions for Chapter 11 End-of-Chapter Problems Problem 11.1. Examples of very slow processes are geological changes that, for example, transform sedimentary deposits into metamorphic rock or mineralize bones to form fossils. Reactions that take a year or a few years include those that age wine and, if continued for too long, ruin it. Fast reactions include almost every reaction in living organisms, because many biochemical pathways must be sensitive to environmental changes in order to maintain the organism (homeostasis). Other very fast reactions are those in combustions and explosions. Problem 11.2. (a) In Investigate This 11.1, the red phenolphthalein color faded more rapidly in the solution with higher base concentration, so we would predict that it would fade faster in a 2.0 M sodium hydroxide solution compared to a 1.0 M solution. (b) By the same reasoning as in part (a), we would expect that the color would fade slower in a 0.10 M sodium hydroxide solution compared to a 1.0 M solution. Problem 11.3. The reaction of hydroxide anions with the colorless form of phenolphthalein is an acid-base reaction transferring the protons from the two acidic –OH groups bonded to the six-membered rings (These react like phenol; see Table 6.2.) to hydroxide ions. The dianion rearranges to the more stable red form with more pi-electron delocalization over the entire structure. C O O C C O C OH HO O O O (aq) (aq) + 2OH (aq) + 2H 2 O (l) colorless red C O C O O O (aq) + 2H 2 O (l) Problem 11.4. The rate of a chemical reaction refers to the change of concentrations of reactants and products as a function of time. Rate is a change per time. The measurement of any variable that is proportional to a reactant or product concentration as a function of time, can be used to characterize the rate of the reaction. Problem 11.5. (a) In the stroboscopic study of the bombardier beetle shown in the chapter opening illustration, there are about seven frames between the beginning of the first discharge and the beginning of the second. Since the frames are taken every 0.00025 seconds (0.25 ms), the time between discharges is about 0.00175 s [= (7 frames)(0.00025 s·frame –1 )]. The rate of discharge is the inverse of time between discharges: rate = (1 discharge) (0.00175 s) 570 discharge·s –1 . (b) The rate of discharge of the beetle would produce disturbances in the air around the beetle at a frequency of 570 s –1 , which is in the range of human hearing. Audio recordings of the sound the beetle makes show that the sound is produced at the frequency of the discharge. ACS Chemistry FROG 63
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Reaction Pathways Chapter 11 Problem 11.6. The reaction that turns the phenolphthalein red is an acid-base reaction (Problem 11.3), transfer of protons from the acid (phenolphthalein) to the base (hydroxide anion). Proton transfers are almost always quite rapid. The reaction that produces the colorless form of phenolphthalein from its red dianion is between a nucleophile (the hydroxide anion) and an electrophilic center at the middle of the dianion. Nucleophile-electrophile reactions are not always fast and this one
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This note was uploaded on 02/23/2012 for the course CHEM AP taught by Professor Hx during the Fall '11 term at Manitoba.

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Chapter11 - Chapter 11 Reaction Pathways Solutions for...

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