Physical chemistr Reaction Kinetics(3) Xuan Cheng Xiamen University
1 Reaction Kinetics (3) Xuan Cheng Xiamen University Physical Chemistry
Ch ical chemistr Reaction Kinetic Determination of the rate law 1. Half-life method The rate law r=kA] [B].m (1748) /2 Forn≠1 (n-DA1- (17.29 2 og1041/2=g10 (n-1)logIoLAlo (17.49 (n-1) log101/2 g10 1-n)logIo[A] (1749)
2 Determination of the Rate Law Physical Chemistry The rate law r = k[A] [B] [L] (17.48) 1. Half-life method o A n n A n k t ( 1)log [ ] ( 1) 2 1 log log 10 1 10 1/ 2 10 − − − − = − (17.49) A n o n n A k t 1 1 1/ 2 ( 1) 2 1 − − − − = For n 1 (17.29) o A n n A n k t (1 )log [ ] ( 1) 2 1 log log 10 1 10 1/ 2 10 + − − − = − (17.49) Reaction Kinetics
Ch ical chemistr Reaction Kinetic 半衰期法确定反应级数 用半衰期法求除一级反应以外的其它反应的级数。 根据n级反应的半衰期通式:2联两个不同起始 浓度1A7o,4作实验,分别测定半衰期为1和 因過同一反应,常数相同,所以 h(1/2/1/2) n=1+ 1/2 In(Alo/Alo) h/2=hK+(1-m)n 以nt1~ln47作图从直线斜率求n值。从多个实验数据 用作图法求出的n值更加准确
3 半衰期法确定反应级数 用半衰期法求除一级反应以外的其它反应的级数。 以lnt1/2～ln[A]o作图从直线斜率求n值。从多个实验数据 用作图法求出的n值更加准确。 根据 n 级反应的半衰期通式： 取两个不同起始 浓度[A]o，[A]o ’作实验，分别测定半衰期为t1/2和 ， 因为同一反应，常数相同，所以： 1 1 1/ 2 [ ] 1 ( 1) 2 1 − − − − = n A o n n k A t 1/ 2 t ' Physical Chemistry 1 1/ 2 1/ 2 [ ] [ ] ' ' − = n o o A A t t ln([ ] '/[ ] ) ln( / ' ) 1 1/ 2 1/ 2 A o A o t t n = + A o ln t ln K (1 n)ln[ ] 1/ 2 = + − Reaction Kinetics
Ch ical chemistr Reaction Kinetic Determination of the rate law 2. Powell-plot method r=k[4 C≡ O p≡kA[A (17.50) the fraction of a unreacted +[B-(n-1) kgt For n≠1(1728 k Forn=1(17.13 C Forn≠ In a=-o For n=1 (17.51)
4 Physical Chemistry Determination of the Rate Law 2. Powell-plot method A A o [ ]/[ ] n r = k[A] (17.50) the fraction of A unreacted k A t n A o 1 [ ] − A n k t A A A n o n o 1 ( 1) 1 1 = + − − − For n 1 (17.28) 1 ( 1) 1 − = − − n n For n 1 (17.13) k t A A A o ln = − For n = 1 ln = − For n = 1 (17.51) Reaction Kinetics
Ch ical chemistr Reaction Kinetic Determination of the rate law Forn≠1 In a For (17.51) For a given n, there is a fixed relation between a and o for every reaction of order n Plot a versus logroo for commonly occurring values of n to give a series of master curves. (Fig. 17.6) The Powell-plot method requires the initial investment of time needed to make the master plots Table 17.1 gives the data needed to make the master plots
5 Physical Chemistry Determination of the Rate Law 1 ( 1) 1 − = − − n n For n 1 ln = − For n = 1 (17.51) For a given n, there is a fixed relation between and for every reaction of order n. Plot versus log10 for commonly occurring values of n to give a series of master curves. (Fig. 17.6) The Powell-plot method requires the initial investment of time needed to make the master plots. Table 17.1 gives the data needed to make the master plots. Reaction Kinetics