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Questions
Distinguish between Order and Molecularity of reaction.
Differentiate between order of a reaction and its molecularity.
How does order of a reaction differ from the molecularity of the reaction?
Give one difference between the order of a reaction and its molecularity.
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Solution 1
| Order | Molecularity | |
| i. | It is an experimentally determined property. | It is a theoretical entity. |
| ii. | It is the sum of the powers of the concentration terms of the reactants that appear in the rate equation. | It is the number of reactant molecules taking part in an elementary reaction. |
| iii. | It may be an integer, fraction, or zero. | It is an integer. |
| iv. | It is not based on a balanced chemical equation. | It is based on a balanced chemical equation. |
Solution 2
| Sr. No. | Order of reaction | Molecularity of reaction |
| 1. | It is the sum of the concentration terms on which the rate of reaction actually depends, or it is the sum of the exponents of the concentrations in the rate law equation. | It is the number of atoms, ions, or molecules that must collide with one another simultaneously so as to result in a chemical reaction. |
| 2. | It need not be a whole number, i.e., it can be fractional as well as zero. | It is always a whole number. |
| 3. | Only experimentation can determine it; calculation is not possible. | You can calculate it by simply adding the molecules from the slowest step. |
| 4. | It is an overall reaction, and no separate steps are written to obtain it. | The overall molecularity of a complex reaction has no significance. It is the only slowest step whose molecularity has significance for the overall reaction. |
| 5. | Even the order of a simple reaction may not be equal to the number of molecules in the reactants, as seen by the unbalanced equation. | Typically, the stoichiometry of the equation provides the molecularity for simple reactions. |
| 6. | It may be an integer, fraction, or zero. | It is always an integer and never a fraction or zero. |
Notes
Students should refer to the answer according to their questions.
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