Characteristics Of Reaction Order

Order of a reaction is an experimental term. It can not be directly determined by the observed rate law. In order to determine the reaction order, the rate law expression of the reaction must be known.

Generally, The term 'Reaction Order' (or sequence of reaction) refers to how the concentration of one or more reactants directly affects the rate of the reaction. Thus, it expresses how much the concentration of reactant can affect the rate of reaction. 

........."The Order Of The Reaction Can Be In The Form Of An Integer Or A Fractional Value. Its Value Can Also Be Zero"..........

Order Of A Reaction??

Reaction order for a chemical reaction is defined as; "The sum of the exponents to which the concentration of reactants are raised in the rate law, is called as order of the reaction". 

                             Or

"The summation of exponents of all the reactant's concentration term present in the rate law obtained from the rate determining step is called as an order of reaction".

Depending on the concentration of the reactants, the reactions can be zero order, first order, second order, pseudo first order, etc. One can predict the order of reaction by units of rate constant.

Characteristics Of Reaction Order

There are some characteristics of the order of reaction which are as follows;

• Order of a reaction represents the number of reactant entities whose concentration directly affect the reaction rate.
• Reaction order is obtained by simply adding the exponents of the reactant's concentration term present in the rate law. 
• Reaction order is obtained by reactant's concentration only and it is unaffected by the product's concentration. 
• Order of a reaction is an experimental determined term.
• Overall order of a reaction is equal to the sum of all the individual orders correspond to each reactant. 
• Reaction order may be equal to zero or any positive/negative integer or fractional value.  
• For a complex reaction, the reaction's order is obtained by rate determining step.
• Reaction's order tells us how the rate of reaction is affected by the concentration of it's reactants. 
• Reaction's order depends on the operating condition like pressure,temperature and concentration. 
• The order of the reaction does not depend on the stoichiometric coefficients of the reactants present in the balanced chemical equation.

Points to be remembered

➩ For a complex reaction, the order of reaction is finding out by using rate determining step (the slowest step in reaction mechanism). While in case of simple reaction in which the reaction is completed in a single elementary step, the order of a reaction is directly determined by the experimental rate law. 

➩ For a complex reaction, the order and the molecularity of a reaction is identical and individual orders are equal to the stoichiometric coefficients of reactants.

➩ As we know the order of reaction is of any integer value as well as fractional value. The possible orders are;

1. Zero - In which the rate of reaction is independent of the reactant's concentration. 
2. Negative integer - In which rate of reaction is inversely affected by the reactant's concentration.
3. Positive integer - In which rate of reaction is directly affected by the reactant's concentration. 
4. Fractional value - In which a rate of reaction related to reactant's concentration in a more complexity manner. Generally, a fractional value of the order of the reaction is possible in complex reactions.

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