化学动力学一.ppt

Examination: (1) The intensity of some UV spectra for NO at room temperature increase with the increasing of pressure of NO indicated that N2O2 was formed at low temperature. (2) Explain the negative activation energy The reaction rate for NO2+O2→2NO2 increases with increase in temperature, but the formation of N2O2 is exothermic reaction, the increase of temperature is suitable for equilibrium of the formation of NO which leads to the concentration of N2O2 decrease obviously, thus exhibits the reaction rate decreases with increase of reaction temperatures. p764 Thermal decomposition of ethane： C2H6→C2H4+H2 ∵ 链引发反应，k1一般不大，忽略不计. Exercise: p781 31、32、34、41 46.1 17.2 11.5 5.7 4.0 -0.4 Ea,1 - Ea,2 /kJ·mol-1 0 10-3 7 ?10-3 0.08 0.13 0.67 ymax / a 10-7 7?10-3 0.047 0.25 0.40 2.01 tmax 108 103 100 10 5 1/5 k1 / k2 When k2 k1, ymax would be very small, and the tmax would be very short. A B C k1 k2 The physical meaning of k2 k1 B is a active intermediate, it is difficult to form but easy to decompose to product. active intermediate Active atom: Cl, H, etc. Radicals: CH3?, H2C:, C+, C-, etc. Activated molecules: A* When k2 k1 The total rate only determined by k1 When k2 k1 The total rate only determined by k2 The rate of the overall consecutive reaction is seen to depend only on the smaller rate coefficient. The step with the slowest rate is called the rate-determining step (r. d. s.). Synthesis of ammonia 1) Absorption → 2) activation → 3) reduction → 4) protonation → 5) desorption Optimization of the reaction conditions 习题：P777 18、19、20、21 §8 反应机理初步 认识反应的关键控制步骤，以便控制整个化学反应朝着有利于我们所需要的方向进行； 反应机理是关于化学反应历程的一种推断或假设； 假设或推断必须经过严格的实验验证； 由于机理研究的复杂性，有时需要采用一些估计的方法 Stationary-state approximation; r. d. s. approximation Equilibrium approximation In 1919, J. A. Christiansen, K. F. Herzfeld and M. Polanyi independently proposed the mechanism consisting of five elementary reactions as