Module 6 :  Reaction Kinetics and Dynamics
Lecture 30 : Complex Reactions
 
   Recap
   In this Lecture you have learnt the following
  Summary
  In this lecture, we have described the kinetics and mechanisms of reactions which are often classified as complex. Chain reactions and polymerization reactions involve a large number of repeated steps. Steady state approximations can also be used here whenever the intermediates (such as radicals) are short lived. Explosions occur when the rates of one or more steps of a reaction increase suddenly and when the heat produced in the reaction is so large that the container can not accommodate it.
   
  Photochemical reactions are induced by light. The excited states are quite reactive and can induce a number of reactions like associations, dissociations, ionizations, and so on. Quantum yield or quantum efficiency is the number of reactant molecules reacted per each photon absorbed . In photosynthesis, the quantum efficiency is about 10%. Chemical oscillations are a fascinating class of reactions which involve autocatalysis, more than one steady state and wherein, the reaction conditions are far away from equilibrium.
   
 

The last section dealt with homogeneous (one phase) and heterogeneous (more than one phase) catalysis. Catalysts reduce the activation energy and enhance the reaction rate without taking part in the reaction stoichiometry. They generally alter the reaction mechanism by providing a fascile path for the reaction to occur.

   
   
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