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Experiment 8

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 chemical reaction. 2. To understand the general theories and methods of

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Experiment 8

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  1. Experiment 8 The Rate of Chemical Reaction and Activation Energy

  2. Purposes 1. To verify the effects of the concentration， temperature，and catalyst on the rate of chemical reaction. 2. To understand the general theories and methods of determining the reaction rate、 the reaction order、 the rate constant and activation energy of the reaction. 3. To learn the usage ofgeneral theories and methods of electromagnetic stirrer and thermostatic waterbath.

  3. Principles (NH4)2S2O8 + 2KI ＝ (NH4)2SO4 + K2SO4 + I2 or (1) slow (2) fast 1mol S2O82- ～1mol I3-～ 2mol S2O32-

  4. 1 lgv = lgk + m lg[S2O82-] + n lg[I-]

  5. lgv = lgk + m lg[S2O82-] + n lg[I-] When [I-] is kept constant, the plot of lgv versus lg[S2O82-] 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 lg[I-] is also a straight line and its slope n is the reaction order of [I-]. The total reaction order (m + n) can be calculated 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-]m[I-]n.

  6. Plot lgk versus 1/T yields a straight line. The activation energy of the reaction can be determined from the slope of the line.

  7. 0.010mol·L-1 Na2S2O3溶液 0.4%淀粉 溶液 Procedure 1.ｃ－v 0.20mol·L-1(NH4)2S2O8 溶液 0.20mol·L-1 KI溶液 快速 同时启动秒表， 并不断搅拌 混合均匀 当溶液刚出现蓝色， 立即停表计时

  8. 0.20mol·L-1 KI溶液 ① 0.010mol·L-1 Na2S2O3溶液 ② ③ 0.4%淀粉 溶液 2. T－v 0.20mol·L-1(NH4)2S2O8 溶液 快速 ④ 室温：T 水浴：T+10 冰浴：T-10 同时启动秒表， 并不断搅拌 混合均匀 记录反应时间 和温度 启动秒表 按表中编号进行实验： 2(室温)、6(升温)、7(降温)

  9. 3. catalyst－v 2滴0.02mol.L-1 Cu(NO3)2溶液 0.20mol.L-1 (NH4)2S2O8 搅拌 0.20mol.L-1KI 0.4%淀粉溶液 0.20mol.L-1KNO3 0.010mol.L-1Na2S2O3 迅速 混合 搅拌 计时

  10. 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 =k·cm(S2O82－)·cn(I-)即可求得反应速率常数k。

  11. 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。

  12. 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。

  13. NEXT EXPERIMENTExpt 22 Expt 23

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