武汉大学：《物理化学 Physical Chemistry》课程教学资源（PPT课件讲稿）12 The rate theory of unimolecular reaction

The rate theory of unimolecular reaction 单分子反应速率理论 Mechanism of Complex reactions 复杂反应

The rate theory of unimolecular reaction 单分子反应速率理论 Mechanism of Complex Reactions 复杂反应

SC. TST bimolecular reaction collide with each other 双分子反应--碰撞 Unimolecular reaction 单分子反应,HOW?

SCT, TST ----- bimolecular reaction collide with each other 双分子反应 ----- 碰撞 Unimolecular reaction? 单分子反应, HOW?

History O At early 19th century, of first-order. O Single molecule at ground state will not undergo any reaction O how do reactant molecules attain necessary energy of activation O In 1919, Perrin-radiation activation theory. problem: radiation from the wall is not high enough

At early 19th century, of first-order. History: Single molecule at ground state will not undergo any reaction how do reactant molecules attain necessary energy of activation In 1919, Perrin – radiation activation theory. problem: radiation from the wall is not high enough

of second-order at low pressure, first order at high pressure. 1921. Christiansen have to be collision [A]

of second-order at low pressure, first￾order at high pressure. have to be “collision” 1921, Christiansen

In 1922. Lindemann and christiansen: The activated molecules react long after the collision. There is a time lag between activation and reaction 时滞 some of them may lose their energy due to the further collision (deactivation). Only part of the activated molecules can form product 部分失活(稳定化) 碰撞活化 部分反应(产物)

In 1922, Lindemann and Christiansen: The activated molecules react long after the collision. There is a time lag between activation and reaction. some of them may lose their energy due to the further collision (deactivation). Only part of the activated molecules can form product. 时滞 碰撞活化 一部分失活(稳定化) 一部分反应(产物)

Lindemann mechanism Ku A+ M A+ M

A + M A* + M k1 k-1 P k2 Lindemann mechanism

da klA 三K2 stationary- state approximation稳态近似 处理短寿命的“中间体” 浓度不随时间变化 dlA 0

[ ] [ ] * 2 * k A dt d A r = − = stationary-state approximation 稳态近似 处理短寿命的“中间体”: 浓度不随时间变化 0 [ ] * = dt d A

Lindemann mechanism Ku A+ M A+ M P dAl dtKLAJIM][A]=0

A + M A* + M k1 k-1 P k2 Lindemann mechanism * * * 1 1 2 [ ] [ ][ ] [ ][ ] [ ] 0 d A k A M k A M k A dt = − − = −

[a)≈k[AI[M] k1[M]+k2 da k2[A] K,kALli k1[M]+

1 2 * 1 [ ] [ ][ ] [ ] k M k k A M A + = − 1 2 1 2 [ ] [ ][ ] k M k k k A M r + = − [ ] [ ] * 2 * k A dt d A r = − =

Case I: pressure is low enough: k1[M门]<<k2 碰撞失活远小于反应 K,kLAMi 三 k1[M]+k2 二级反应 r=KLAILMI

Case I: pressure is low enough: 1 2 k [M] k − 1 2 1 2 [ ] [ ][ ] k M k k k A M r + = − [ ][ ] r = k1 A M 碰撞失活 远小于 反应 二级反应