Question

Explain the method of initial rates to determine rate law and order of reaction.

Answer 1

The factors that affect the rate of reaction are temperature, concentration, pressure and presence of catalyst. At a microscopic level, we are interested in amounts reacted and formed. And at the molecular level, we are going to discuss about reaction mechanism that involves orientation and energy of molecules that undergoes collisions

Complete step by step answer:
Rate law is defined as an equation that gives a relationship between the concentration of the reactant and rate of a reaction. The reaction rate is defined as the product of molar concentration of each reaction, which is raised to some power, which may or may not be the stoichiometric coefficient of the reacting species.
For example, $2N{{O}_{(g)}}+{{O}_{2(g)}}\to 2N{{O}_{2(g)}}$
$Rate=k{{[NO]}^{2}}[{{O}_{2}}]$
where, $k$ is the rate constant.
The rate law expression can be written in differential form:
$\dfrac{-d[R]}{dt}=k{{[NO]}^{2}}[{{O}_{2}}]$
The order of reaction is defined as the power of the concentration of each reactant. In first order kinetics, the rate is only dependent on the concentration of single species. The overall order of the reaction can be calculated by the addition of individual orders.
For example, let us write a generalized chemical equation:
$aA+bB\to cC+dD$
Where $a,b,c,d$ are the stoichiometric coefficients of the reactants and products.
$Rate=k{{[A]}^{x}}{{[B]}^{y}}$
where, $x$ and $y$ are the order of $A$ and $B$ respectively.
The overall order of reaction is equal to the addition of $x$ and $y$
Order of a reaction can be an integer value or a fractional value.
In zero order reaction, rate of reaction is independent of the concentration of the reactant.

Note: Order of reaction is defined as the sum of the power of the concentration of reactants.
The overall order can be an integer value or a fractional value.
For elementary reaction, the value of molecularity and order are equal.