Difference Between Elementry Reaction and Non-Elementry Reaction

The difference between elementary and non-elementary reactions lies in their complexity and definitions in simple words.

Elementary Reactions

Such reactions in which the rate of reaction is equal to the stoichiometry equation are called elementary reactions. For elemental reactions, the order of each reactant is equal to the stoichiometry coefficient. The order of the elementary reaction is not more than three.

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For Irreversible elementary reaction

a. A + b.B →r.R

The rate equation is 

-r_A = K C^a_A * C^b_A

r_A = - K C^a_A * C^b_A

1. This is a single-step reaction. 

2. Elementary reactions are simple in nature. 

3. The order of an elementary reaction is equal to the stoichiometry coefficient. 

4. The order of the elementary reaction is always an integer. 

5. For elementary reaction 2A R The rate law is 

-r_A=KC^2_A

6. Example of elementary reaction. 

C2H5OH + CH3COOH ⟶ CH3COOC2H5 + H2O

Non-Elementary Reaction

Such reactions in which the rate equation is not equivalent to the stoichiometry equation are called non-elementary reactions. 

H2 + Br2 ⟶ 2HBr

The rate equation

r_(HBr) = {K_1 (H_2) (Br_2)^(1/2)} / {K_2 {(HBr)/(Br_2)}

In non-elemental reactions, there is no direct relationship between the reaction order and the stoichiometry coefficient.

1. This is a multiple-step reaction. 

3. It is complex in nature. 

4. Where the order and stoichiometry coefficient of these reactions differ. 

5. Where the order of these reactions can be integer or friction. 

6. For non-elementary reaction 2B=S 

7. The rate law is 

-r_B = KC_B^2

8. Example of non-elementary reaction 

H2 + Br ⟶ 2HBr

Main Difference 

Feature	Elementary Reaction	Non-elementary Reaction
Number of steps	One	Two or more
Intermediates	None	Present and detectable
Rate law	Simple, integer order	Complex, may have fractional order
Example	2NO2 -> 2NO + O2	Decomposition of ozone

What is the difference between an elementary process and a regular chemical reaction?

An elementary process occurs in a single step with no detectable intermediates, whereas a regular chemical reaction can be a single step or a series of steps with intermediates.

> Concentration Dependent Term of a Rate Equation 

Kinetic View of Equilibrium for Elementary Reaction Formula