553 CHAPTER 14 Chemical Kinetics: The Rates of Chemical Reactions trans-fColenhal.(aq) + H2O(C) â (see Section 4-8), and some data collected by that approach are given below. The initial concentrations were Iphenolphthalein] -0.0050 moUL and TOH 1 0.61 moVL (Data are taken from review materials for kinetics at chemed.chem.purdue.edu.) (For more details on this reaction see L. Nicholson, Jourmal of Chemical Edacation, Vol 66, p. 725, 1989.) red The reaction progress is olowed by observing the of the solution. The original solution is green, and the final solution is red, but at some intermediate stage when is gray. Time ts) 0.00 0.0050 223 35.7 1.1 69.3 91.6 1204 160.9 2303 299.6 0.0035 0.0025 00015 0.0010 0.00050 000025 (a) Plot the data above as Iphenolphthalein] versus time, and determine the average rate from t15 seconds and from -125 seconds. Des the rate change? If so, why? 0 to 100 seconds to original solution intermedlate solution (b) What is the instantaneous rate at 50 seconds? (c) Use a graphical method to determine the order of the d) What is the half-life for the reaction? green, cobalt-based complex called trans-dichlorobis- reaction with respect to phenolphthalein. Write the rate law, and determine the rate constant. 82. You want to study the hydrolysis of the beautiful ethylenediamine)cobaltiIII) ion final solution Changes in color with time as CI- ion is replaced by H,O in a cobalt(Il) complex. The shape in the middle of the beaker is a vortex that arises because the solutions are being stirred us- ing a magnetic stirring bar in the bottom of the beaker Reactions such as this have been studied extensively, and that the initial, slow step in the reac- tion is the breaking of the Co-Cl bond to give a five- coordinate intermediate. The intermediate is then attacked rapidly by water Slow: trins-Co(enhal.(aq) â In this hydrolysis reaction, the green complex ion trans- Colen Cll forms the red complex ion [ColembalHO) [Co(enhci (aq) + a-(aq) cip as a Cl ion is replaced with a waser molecule on the Co- ion (en-H:NCH CHINH
