1. 胡适：对于各种知识无所不知，无所不晓，然后做学 问才能有成绩。 年 J. H. Newman 《大学教育目的的本质讨论》： 对学生传授所有领域的知识，发展学生的智力，才是 对未来最好的准备。 3.Harvard Univ.: Enter to grow in wisdom.

10.8 Kinetics of reaction in solution

Solvents 10 2 k / dm 3  mol -1  s -1 Hexane Benzene chlorobenzene0.023 nitrobenzene70.1 If the polarity of product is higher than that of reactants, higher polar solvent benefits the reaction. 1) Solvent effects on rate constants The reaction rate depends strongly on the solvent used.

Solvent effect on activation energy standard Solvent A Solvent B

For evaluation of solvent effect

3) Effect of ionic strength-primary/kinetics salt effect For ionic reactions in solution, activity coefficients must be taken into consideration. Therefore, the apparent rate constant depends on the ionic strength of the solution. For dilute solution

Effect of ionic strength on the rate of reaction between two ions. +4: Co(NH 3 ) 5 Br 2+ + Hg 2+ +2: S 2 O I  +1: [NO 2 NCO 2 C 2 H 5 ]  + OH  0: CH 3 COOC 2 H 5 + OH  -1: H 2 O 2 + H + + Br  -2: Co(NH 3 ) 5 Br 2+ + OH  A substantial amount of inert salt (supporting electrolyte) was added to keep the ionic strength and therefore the activity coefficient of the solution essentially constant.

4) Cage effect Solvent cage: capture reactant molecules Diffuse in or out, from or to other solvent cages. Once reactant molecules meet in one solvent cage through diffusion (an encounter), they will be trapped in the cage for a relatively long time during which they collide repeatedly with each other (collision), providing more chance to react. Within a solvent cage (for 1~100 ns), two reactant molecules can collide 10 ~10 5 times. Does viscosity of solvent affect collision in the solvent cage? Experimental evidence: photolysis of CH 3 NNCH 3 and CD 3 NNCD 3 in gaseous phase and in solution. Given by Lyon and Levy in 1961.

The process can be represented as A + B → {AB} → products in which the {AB} term represents the caged reactants including the encounter pair and the activated complex ~ s, collides for 10 ~ 10 5 times. E re > E diff. Reaction control. E diff. > E re, diffusion control.

5) Diffusion-controlled reactions diffusion reaction

Discussion: If reaction is much slow than diffusion, activation control or kinetics control If diffusion is much slow than reaction, diffusion control

For activation control Resembles gaseous reaction, no effect of solvent. mediagasCS 2 C6H6C6H6 C 2 H 5 OH 10 6 k/ dm 3  mol -1  s Solvent effect on reaction between species of low polarity is weak.

For diffusion control Fickian first lawFlux D diffusion coefficient with unit of m 2  s -1. For spherical particle, Einstein-Storks equation For second-order reaction Integration yields

For second-order reaction f is electrostatic factor. Diffusion-Limited Rate Constants, Slow reactions

If r A = r B For diffusion, E a  10 kJ  mol -1

2) Catalysis of water

Solvent effects 1)Solvation of reactant 2)Catalysis 3)Intermolecular intereaction (ions, polar reactant) 4)Diffusion (solvent viscosity) 5)Hydrogen bond Change mechanism