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Half-life of a Reaction The half-life, t1/2, of a reaction is the amount of time it will take the concentration, [A], of a reactant to reduce to half its initial concentration, [Ao]. That is to say,               @ t1/2, [A] = [Ao]/2 ...……(i) The half-life of the various orders of reaction can be calculated by substituting the above equation into the respective integrated rate laws. ( a) Half-life of a Zeroth-Order Reaction Recall that the zeroth-order integrated rate law is given by:                  [A] = [Ao] - kt …………(ii)                  [Ao] - [A] = kt @ t1/2, [A] = [Ao]/2                  kt1/2 = [Ao] - ([Ao]/2)                  kt1/2 = (2[Ao] - [Ao])/2                  kt1/2 = [Ao]/2                    t1 /2 = [ Ao ]/2k …………(iii) Equation (iii) above, gives the half-life for a zeroth-order reaction, which can be obtained by finding the product of half the initial reactant concentration and the reciprocal of the reaction rate constant ([Ao]/2 × 1/k). (b) H alf-

In our previous post, we looked at the overview of the rates of chemical reactions, where we studied the concepts and factors that affect the rates of reactions. In this post, we will be studying the rate law and the different orders of reaction, and how to determine them. Rate Law Consider the reaction:             mA + nB ----> Products The rate law states that the rate of a reaction is directly proportional to the active masses of the reactants. This implies that the concentration of the reacting species will determine how fast and how far a reaction can go. Using the above equation, the rate law can be expressed as:             rate & [A]^m[B]^n ..........(i)             rate = k[A]^m[B]^n ..........(ii) where, [A] = concentration of reactant A [B] = concentration of reactant B    & = sign of proportionality    k = rate constant The rate law is also known as the law of mass action. Orders of Reaction In chemical kinetics, an order is the index or power of t