Question

Explain the initial rate method.

Answer 1

Hint: For answering the initial rate method we need to refer to the rate law of chemical kinetics. By referring to its name we can understand that it is the method which involves measurement of the initial rate of a reaction. And the measurement is continuously repeated for a few sets of initial concentration to keep a check how the reaction rate varies.

Complete step by step answer:
We know that the method of initial rates is a technique used for deriving the rate laws. From the name we can derive that, it is the method which measures the initial rate of a reaction. We can accomplish this by determining the time needed to exhaust a particular amount of a reactant.
Let’s consider the reaction $A + B \to $ products
So, the formula of the rate law is
rate = k\[{[A]^\alpha }{[B]^\beta }\]
Now, let’s determine the ratio between i and j to determine the relationship
$\dfrac{{rat{e_i}}}{{rat{e_j}}} = \dfrac{{k{{[A]}_i}^\alpha {{[B]}_i}^\beta }}{{k{{[A]}_j}^\alpha {{[B]}_j}^\beta }}$
Thus, the method of initial rates is the process of determining the rate law of a chemical reaction. For determining this we need the activation energy of the reaction by finding the value of the rate constant, ‘k’ at several temperatures. Here, the initial rate of a reaction is the instantaneous rate at the start of the reaction i.e., t = 0. So, the initial rate of the reaction is equal to the negative of the slope of the curve of reactant concentration versus time at t = 0.

Note:
The usefulness of the initial rate method is that we can determine the order of a reaction if a reaction involves more than one reactant. The dimensions of rate constant, k are\[L{\text{ }}mo{l^{-1}}\;{s^{-1}}\].