Example 3.8

Example . Table . summarises the mathematical features of integrated laws of zero and first order reactions. Table . : Integrated Rate Laws for the Reactions of Zero and First Order Order Differential Integrated Straight Half- Units of k type rate law rate law line plot life R ® P d[R]/d t = - k kt = [R] -[R] [R] vs t [R] / k conc time - or mol L – s – R ® P d[R]/d t = - k [R] [R] = [R] e - kt ln[R] vs t ln / k time - or s – or kt = ln{[R] /[R]} Most of the chemical reactions are accelerated by increase in temperature. For example, in decomposition of N O , the time taken for half of the original amount of material to decompose is min at o C, h at o C and days at o C. You also know that in a mixture of potassium permanganate (KMnO ) and oxalic acid (H C O ), potassium permanganate gets decolourised faster at a higher temperature than that at a lower temperature. It has been found that for a chemical reaction with rise in temperature by °, the rate constant is nearly doubled. The temperature dependence of the rate of a chemical reaction can be accurately explained by Arrhenius equation ( . ). It was first proposed by Dutch chemist, J.H. van’t Hoff but Swedish chemist, Arrhenius provided its physical justification and interpretation.