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1、Experiment 8,The Rate of Chemical Reaction and Activation Energy,Purposes,1. To verify the effects of the concentration，temperature，and catalyst on the rate of chemicalreaction. 2. To understand the general theories and methods ofdetermining the reaction rate、 the reaction order、the rate constant an
2、d activation energy of thereaction. 3. To learn the usage of general theories and methodsof electromagnetic stirrer and thermostaticwaterbath.,Principles,(NH4)2S2O8 + 2KI (NH4)2SO4 + K2SO4 + I2,or,(1) slow,(2) fast,1mol S2O82- 1mol I3- 2mol S2O32-,lgv = lgk + m lgS2O82- + n lgI-,1,lgv = lgk + m lgS2
3、O82- + n lgI-,When I- is kept constant, the plot of lgv versus lgS2O82- is a straight line. The slope of the line m is the reaction order of S2O82-. Similarly when S2O82- is kept constant, the plot of lgv versus lgI- is also a straight line and its slope n is thereaction order of I-. The total react
4、ion order (m + n) can becalculated from m and n. When we know m and n, the constant k of the reaction rate at a given temperature can be determined from reaction rate equation v = k S2O82-mI-n.,Plot lgk versus 1/T yields a straight line. The activation energy of the reaction canbe determined from th
5、e slope of the line.,Procedure,1.v,混合均匀,当溶液刚出现蓝色， 立即停表计时,同时启动秒表， 并不断搅拌,0.20molL-1 KI溶液,0.20molL-1(NH4)2S2O8 溶液,快速,2. Tv,启动秒表,记录反应时间 和温度,同时启动秒表， 并不断搅拌,室温：T 水浴：T+10 冰浴：T-10,0.20molL-1(NH4)2S2O8 溶液,快速,混合均匀,按表中编号进行实验： 2(室温)、6(升温)、7(降温),3. catalystv,迅速 混合,搅拌 计时,2滴0.02mol.L-1 Cu(NO3)2溶液,0.20mol.L-1 (NH4)2
6、S2O8,搅拌,0.20mol.L-1KI 0.4%淀粉溶液 0.20mol.L-1KNO3 0.010mol.L-1Na2S2O3,实验数据处理,1、反应级数和反应速率常数的计算 将反应速率表示式v =k cm(S2O82)cn(I-)两边取对数：lgv = mlgc (S2O82) + nlgc(I-) + lgk当c (I-)不变：以lgv对lgc (S2O82)作图，可得一直线，斜率即为m。当c (S2O82)不变：以lgv对lgc (I-) 作图，可求得n。总反应级数则为（m+ n）。将求得的m和n代v =kc m(S2O82)c n(I-)即可求得反应速率常数k。,2、求反应的活化能,反应速率常数k与温度T之间的关系为：,测出不同温度时的k值，以lg k对1/T作图，可得一直线 由直线斜率(-Ea/2.303R), 求得反应的活化能Ea。,实验注意事项 实验中所用溶液的浓度要准确，因此各试剂的取用 要专管专用，不要污染试剂，从而改变试剂的浓度。 反应时，溶液要快速加入，同时启动秒表。,NEXT EXPERIMENT Expt 22 Expt 23,
