Question

What is rate constant? Write “two applications” of rate constant

Answer 1

The rate law expression has a term K which relates the rate of the reaction with concentration of reactants. Rate constant depends on temperature and catalyst. With increase in temperature, the constant will also increase.

Complete step by step answer:
Chemical kinetics deals with the measurement of rate of a reaction
Rate of a reaction is the speed at which the chemical reaction proceeds or rate of a reaction is nothing but change in concentration with time
${{Rate = }}\dfrac{{{{Change\; in \;concentration}}}}{{{{Change\; in\; time}}}}$
Consider a general reaction
${{A}}\xrightarrow{{}}{{P}}$
And the rate can be written as
${{Rate = }}\dfrac{{{{ - d}}{{{C}}_{{A}}}}}{{{{dt}}}}{{ = }}\dfrac{{{{dCp}}}}{{{{dt}}}}$
The negative sign symbolises the decrease in the concentration of reactants
Consider the rate law expression
${{Rate = K}}{\left[ {{R}} \right]^{{{order}}}}$
The proportionality constant K present in the rate law expression relating the rate of a reaction at a given temperature with the concentration of the reactant (in case of unimolecular reaction) or to the product of the concentration of reactants is called rate constant.
If the order of the reaction is 0
Then ${{Rate = K}}{\left[ {{R}} \right]^{{0}}}$
${{Rate = K}}$
Thus for a zero order reaction rate of reaction becomes equal to rate constant of the reaction
Applications of rate constant
The rate of a reaction for the given composition of reaction mixture can be determined by rate constant
It is useful in determining the mechanism of a complex reaction.

Note: Rate constant can also be given as rate of the reaction which has a molar concentration of reactants as unity
In a reaction
${{A + B}} \to {{P}}$
${{r \propto }}{{{C}}_{{A}}}{{{C}}_{{B}}}$
${{r = }}{{{C}}_{{A}}}{{{C}}_{{B}}}$
If ${C_A} = {C_B} = 1$
Then ${{r = K}}$
Change in the concentration of the reactants with time is termed as rate of a reaction. Rate of reaction generally depends on initial concentration of reactant other than zero order reaction but in case of rate constant it is independent of concentration.
The variation of rate constant K is expressed in terms of Arrhenius equation
${{K = A}}{{.}}{{{e}}^{\dfrac{{{{ - E_a}}}}{{{{RT}}}}}}$