Fast Reactions

Fast reactions are those reactions which occur instantaneously. A fast reaction is dependent on the reaction rates. These reactions are so fast that they take place as soon as the reactants are bought near. In general, these reactions involve ionic species and therefore known as ionic reactions. These reactions take around 10-14 to 10-16 seconds for completion. It is very difficult to determine the rates of these reactions. It can be defined as a reaction with a half-life of milliseconds or less; such reactions take place so rapidly that special experimental techniques are needed to observe their rate. The rate of a reaction can be defined in terms of the rates with which the products are formed and the reactants are consumed.

For chemical systems it is common to deal with the concentrations of substances, which can be defined as the amount of substance per unit volume. The reaction rate can be defined then as the concentration of a substance which is consumed or produced in unit time. The half-life of a reactant can be defined as the time which it takes for half of the initial amount to undergo reaction. The half life is independent of the initial amount.  The disadvantage of fast reactions is that the time which it takes to mix reactants or to change the temperature of the system can be significant in comparison with the half-life such that the initial time cannot be measured accurately and the other is that the time it takes to measure the amounts of substances can be comparable with the half-life of the reaction.