which method is easy for calculating order of reaction ?? from chemical kinetics ...
Answers
Answer:
Initial Rate Method
Explanation:
The Order of reaction refers to the relationship between the rate of a chemical reaction and the concentration of the species taking part in it. In order to obtain the reaction order, the rate expression (or the rate equation) of the reaction in question must be obtained.
Once the rate equation is obtained, the entire composition of the mixture of all the species in the reaction can be understood.
Reaction Order
The order of reaction can be defined as the power dependence of rate on the concentration of all reactants. For example, the rate of a first-order reaction is dependent solely on the concentration of one species in the reaction. Some characteristics of the reaction order for a chemical reaction are listed below.
Reaction order represents the number of species whose concentration directly affects the rate of reaction.
It can be obtained by adding all the exponents of the concentration terms in the rate expression.
The order of reaction does not depend on the stoichiometric coefficients corresponding to each species in the balanced reaction.
The reaction order of a chemical reaction is always defined with the help of reactant concentrations and not with product concentrations.
The value of the order of reaction can be in the form of an integer or a fraction. It can even have a value of zero.
In order to determine the reaction order, the power-law form of the rate equation is generally used. The expression of this form of the rate law is given by r = k[A]x[B]y.
In the expression described above, ‘r’ refers to the rate of reaction, ‘k’ is the rate constant of the reaction, [A] and [B] are the concentrations of the reactants. The exponents of the reactant concentrations x and y are referred to as partial orders of the reaction. Therefore, the sum of all the partial orders of the reaction yields the overall order of the reaction.
How to Determine Reaction Order
There are several different methods which can be followed in order to determine the reaction order. Some of these methods are described in this subsection.
Initial Rates Method
First, the natural logarithm form of the power-law expression is obtained. It is given by: ln r = ln k + x.ln[A] + y.ln[B] + ….
The partial order corresponding to each reactant is now calculated by conducting the reaction with varying concentrations of the reactant in question and the concentration of the other reactants kept constant.
If the partial order of A is being determined, the power-law expression of the rate equation now becomes ln r = x.ln[A] + C, where C is a constant.
A graph is now plotted by taking ‘ln r’ as a function of ln[A], the corresponding slope is the partial order, given by x.
Integral Method
The order of reaction obtained from the initial rates method is usually verified using this method.
The measured concentrations of the reactants are compared with the integral form of the rate law.
For example, the rate law for a first-order reaction is verified if the value for ln[A] corresponds to a linear function of time (integrated rate equation of a first-order reaction: ln[A] = -kt + ln[A]0).
Differential Method
This method is the easiest way to obtain the order of reaction
First, the rate expression of the reaction is written (r = k[A]x[B]y..)
The sum of the exponents x+y+… gives the final value of the reaction order.
Apart from these methods, there exist other ways to obtain the reaction order, such as the method of flooding in which the concentration of a single reactant is measured when all the other reactants are present in huge excess.
Different Values of Reaction Order
As discussed earlier, the value of the order of reaction may be in the form of an integer, zero, or a fraction. A graph detailing the reaction rates for different reaction orders can be found below.
Order of Reaction
Chemical reactions can be classified into the following types based on the dependence of the rate on the concentration.
Zero Order Reactions
The rate of reaction is independent of the concentration of the reactants in these reactions.
A change in the concentration of the reactants has no effect on the speed of the reaction
Examples of these types of reactions include the enzyme-catalyzed oxidation of CH3CH2OH (ethanol) to CH3CHO (acetaldehyde).
First-Order Reactions
The rates of these reactions depend on the concentration of only one reactant, i.e. the order of reaction is 1.
In these reactions, there may be multiple reactants present, but only one reactant will be of first-order concentration while the rest of the reactants would be of zero-order concentration.
Example of a first-order reactio