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.
{tocify} $title={Table of Contents}
For Irreversible elementary reaction
a. A + b.B →r.R
-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.