Example 3.1

Example . It can be seen (Table . ) that the average rate falls from . × - mol L - s - to . × - mol L - s - . However, average rate cannot be used to predict the rate of a reaction at a particular instant as it would be constant for the time interval for which it is calculated. So, to express the rate at a particular moment of time we determine the instantaneous rate . It is obtained when we consider the average rate at the smallest time interval say d t ( i.e. when D t approaches zero). Hence, mathematically for an infinitesimally small d t instantaneous rate is given by −∆ av P r ( . ) As D t ® or  inst d d P d d r Table . : Average rates of hydrolysis of butyl chloride [C H CI] t / [C H CI] t / t /s t /s r av × /mol L – s – mol L – mol L – ( )