Question

What is rate constant? Write ‘two applications’ of rate law.

Answer 1

In this question. We are asked to define the rate constant and to write applications of rate law. We have to remember that the units of the rate constant depend on the order of the reaction. We should have knowledge of the rate law expressions while answering this question.

Complete answer:
We will begin by writing a rate law expression for a general reaction,
$A + B \to P$
$r = k\left[ A \right]\left[ B \right]$ (rate law expression)
Where k is the rate constant for the reaction
$\left[ A \right]\,and\left[ B \right]$ are the molar concentration of reactants
Now, considering the molar concentration of all the reactants to be unity.
$\left[ A \right]\,and\left[ B \right]$ $= \,1$
Now, the rate law expression becomes
$r = k$
Hence, now the rate constant is equal to the rate of the reaction.
Rate constant or the specific rate constant is the proportionality constant in the rate law expression that expresses a relation between the rate of the reaction and the concentration of the reacting species. It is called the specific rate constant because it is equal to the rate of the reaction when the concentration of the reactants is taken to be unity. A reaction rate constant quantifies the rate and direction of a chemical reaction. We know that the Rate constant values are temperature dependent.
We are now left with writing the applications of the rate law:
1-Rate law expression can be used to estimate the rate of any reaction for different concentrations of the reactants.
2-The most important application of rate law expression is that it can be used to predict the mechanism of any reaction.

Note: It should be noted that rate law expressions are used to predict whether a given reaction is elementary or complex. The rate law is experimentally determined and can hence be used to predict the relationship between the rate of a reaction and the concentration of the reactants.