Difference Between Order and Molecularity

Main difference

The difference between Order and Molecularity is that the Order of a reaction is the algebraic sum of the powers to which the concentration of atoms is raised in a reaction, while Molecularity is the number of reactants that participate in an elementary reaction indicated by its chemical equation.

Order vs Molecularity

The order of a reaction is the algebraic sum of the powers to which the concentration of atoms is raised in a reaction, while, on the other hand, the molecularity is the number of reactants that participate in a chemical reaction indicated by its chemical equation . The order of a reaction reduces that a single reactant is in excess in a reaction, while on the other hand, in the case of molecularity, there is no such dependency on reactants.

The order of a reaction is usually 1, 2, or 3 or maybe zero or in a fraction or negative, but on the other hand, the molecularity of a reaction can always be in a natural number. The order of a reaction can only be determined by experimenting and cannot be predicted based on the balanced chemical equation, while the molecularity of a reaction can be easily predicted based on its equilibrium equation and complicated experimentation is not required.

The order of a reaction can vary as long as a reaction is subjected to changes in pressure, temperature and concentration, etc. On the contrary, since molecularity is just various reactants that participate in a chemical reaction, which makes it irrelevant for these changes. in the atmosphere and makes it invariable. To calculate the order of a reaction, there is no step that determines the rate and the overall reaction is used to calculate the order of a reaction; however, the rate determination step is used to obtain molecularity and the overall reaction is not required.

There are zero order, first order and second order reactions which are classified according to the order; however, based on molecularity, there are unimolecular reactions, bimolecular reactions, and trimolecular reactions. The order of a reaction applies to both simple and elementary reactions, while molecularity is calculated only for simple reactions, there is no sign of calculating the molecularity of a complex reaction.

Comparison chart

Order molecularity
The algebraic sum of the powers to which the concentration of atoms is raised in a reaction. The number of reactants that participate in a chemical reaction.
Determination
It can only be determined by experimenting No complicated experimentation required
Dependence
The order of a reaction is reduced if a single reactant is in excess Molecularity does not depend on the excess of a reactant.
Value
The order of a reaction is usually 1, 2 or 3 or maybe zero or fractional or negative The molecularity of a reaction can always be in a natural number.
Rate Determination Step
No step that determines the rate and the overall reaction is used to calculate the order of a reaction The rate determination step is used to obtain the molecularity
Effect of external environment
The order of a reaction can vary as long as a reaction is subjected to changes in pressure, temperature, and concentration, etc. The molecularity of a reaction is invariant to these changes in the atmosphere.
Classification of reactions
Reactions are classified according to their order as 

zero order reaction

first order reaction

second order reaction

Reactions are classified according to their molecularity as 

Unimolecular reaction

bimolecular reaction

trimolecular reaction

Request
The order of a reaction applies to a simple, elementary reaction. Molecularity is calculated for simple reactions only there is no sign to calculate the molecularity of a complex reaction
What is the order?

The rate order of a reaction is defined as the algebraic sum of the powers to which the concentration of atoms is raised in a reaction. It is also called the dependence of the potency on the rate of each reactant during the reaction. It is the sum of the exponents of the derivative rate law, and may not depend on the stoichiometric coefficients of each reactant. For this reason, the duty rate is determined experimentally.

It is a quantitative measure regarding the rate of a reaction. The law of the rate is the proposed equation. The order of a reaction is usually 1, 2 or 3 or maybe zero or fractional or negative. The order of the rate of a reaction can only be worked out by experimenting and cannot usually be expected based on the balanced chemical equation. In an example like X + Y + Z → A + B + C, the rate law will conclude as R = k [X] p [Y] q [Z] r.

Where R is shorthand for reaction rate, X, Y, and Z are reactants, p, q, and r are reaction orders for X, Y, and Z. Here, K is taken as a constant of proportionality, reflecting the character of the reaction. reaction. Chemists discuss the sum of p, q, and r as the kinetic direction of the reaction. The order of these values ​​is calculated experimentally.

The order of this reaction will be calculated by considering the overall reaction, as opposed to molecularity, where the steps that determine the rate determine the molecularity. There are several types of reactions according to their order. There are zero order reactions in which the rate of a reaction does not depend on the concentration of reactants. First-order reactions are those that depend on the deliberation of the reactants and correspond to a unimolecular reaction. One second-order reactant or two first-order reactants are the second-order reactions that can depend on the deliberation of these two orders.

The order of a reaction can vary as long as a reaction is subjected to changes in pressure, temperature, and concentration, etc. To calculate the order of a reaction, there is no step that determines the rate, and the general reaction is used to calculate the order of a reaction, and the order of a reaction applies to both simple and elementary reactions.

What is Molecularity?

Molecularity is the number of reactants that participate in a chemical reaction indicated by its chemical equation. In the case of Molecularity, there is no dependence on the excess of reagents as there was in the order of reactions. The molecularity of a reaction can always be in a natural number, since it is the number of reactants in a particular reaction.

The molecularity of a reaction can be easily predicted based on its equilibrium equation and no complicated experimentation is required. It does not depend on the external environment, since it is just a number of reactants that participate in a chemical reaction, which makes it irrelevant to these changes in the atmosphere and makes it invariant. The rate determination step is used to obtain molecularity and the overall reaction is not required.

Based on molecularity, there are unimolecular reactions, bimolecular reactions, and trimolecular reactions. In unimolecular reactions, a single molecule undergoes modifications as the reaction proceeds, and has only one reactant and one rate-determining step. In bimolecular reactions, two reactants are involved and complete the reaction. However, in trimolecular reactions, three reactants are involved in the rate determining step. Molecularity is simply calculated for simple reactions; just that there is no sign of calculating the molecularity of a complex or multi-step reaction.

Key differences
  1. The order of a reaction is the algebraic sum of the powers for the concentration of atoms in a reaction, while the molecularity is just the number of reactants that participate in a chemical reaction.
  2. Zero-order, first-order, and second-order reactions are classified according to order; however, based on molecularity, there are unimolecular reactions, bimolecular reactions, and trimolecular reactions.
  3. The order of a reaction is reduced as if a single reactant were in excess in a reaction, while on the other hand, in the case of molecularity, there is no such dependency on reactants.
  4. The order of a reaction is usually 1, 2, or 3 or can be zero, violation, or negative, but on the other hand, the Molecularity of a reaction can always be in a natural number.
  5. The rate order of a reaction can only be determined by experimenting, while the molecularity of a reaction can be predicted based on its equilibrium equation.
  6. The order of a reaction can vary as long as a reaction is subjected to changes in pressure, temperature, and concentration, etc. Contrary to this, as molecularity is just various reactants that participate in a chemical reaction and are not affected by external environmental conditions. .
  7. There is no one step that determines the rate and the overall reaction is used to calculate the order of a reaction; however, the rate determination step is used to obtain molecularity.
  8. The order of a reaction applies to simple and complex reactions or reactions that are completed in multiple steps, while the molecularity is calculated only for simple reactions.

Final Thoughts

The order of a reaction is the algebraic sum of the powers to which the concentration of atoms is raised in a reaction that can be in fraction or negative number, while molecularity is the number of reagents that participate in an elementary reaction and are in neutral number. .

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