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प्रश्न
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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उत्तर १
| 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. |
उत्तर २
| 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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संबंधित प्रश्न
Answer the following in one or two sentences.
What is the relationship between coefficients of reactants in a balanced equation for an overall reaction and exponents in the rate law? In what case the coefficients are the exponents?
A reaction takes place in two steps:
- \[\ce{NO_{(g)} + Cl2_{(g)} -> NOCl2_{(g)}}\]
- \[\ce{NOCl2_{(g)} + NO_{(g)} -> 2NOCl_{(g)}}\]
- Write the overall reaction.
- Identify the reaction intermediate.
- What is the molecularity of each step?
Which of the following is a unimolecular reaction?
Identify molecularity of following reaction:
\[\ce{C2H5I_{(g)} -> C2H_{4(g)} + HI_{(g)}}\]
Name the slowest step that determines the rate in a complex reaction.
Define molecularity.
Write an expression for instantaneous rate of reaction:
2N2O(g) → 4NO2(g) + O2(g).
What is the order of reaction?
Why is molecularity applicable for only elementary reactions whereas order of a reaction is applicable for elementary and complex reactions? Explain with suitable examples.
For a zero-order reaction, molecularity can never be equal to zero. Explain.
For the elementary reaction
\[\ce{2SO2(g) + O2(g) -> 2SO3(g)}\], identify the correct among the following relations.
For the elementary reaction, \[\ce{3H2_{(g)} + N2_{(g)} -> 2NH3_{(g)}}\] identify the correct relation among the following relations.
For the reaction \[\ce{2NO2 + F2 -> 2NO2F}\], following mechanism has been provided:
\[\ce{NO2 + F2 ->[slow] NO2F + F}\]
\[\ce{NO2 + F ->[fast] NO2F}\]
The rate expression of the above reaction can be written as:
The reaction \[\ce{2NO2Cl_{(g)} -> 2NO2_{(g)} + Cl2_{(g)}}\] takes place in two steps as
(i) \[\ce{NO2Cl_{(g)} -> NO2_{(g)} + Cl_{(g)}}\]
(ii) \[\ce{NO2Cl_{(g)} + Cl_{(g)} -> NO2_{(g)} + Cl2_{(g)}}\]
Identify the reaction intermediate.
A reaction involving two different reactants can never be a ______
Identify the molecularity of following elementary reaction:
NO(g) + O3(g) → NO3(g) + O(g)
The reaction takes place in two steps as
(i) \[\ce{NO2Cl(g) ->[k1] NO2(g) + Cl(g)}\]
(ii) \[\ce{NO2Cl(g) + Cl(g) ->[k2] NO2(g) + Cl2(g)}\]
Identify the reaction intermediate.
A certain reaction occurs in two steps as
(i) \[\ce{2SO2(g) + 2NO2(g) -> 2SO3(g) + 2NO(g)}\]
(ii) \[\ce{2NO(g) + O2(g) -> 2NO2(g)}\]
In the reaction:
What is an elementary reaction?
How does a catalyst differ from reaction intermediate?
A complex chemical reaction takes place in two steps.
Step I: NO(g) + O3(g) → NO3(g) + O(g)
Step II: NO3(g) + O(g) → NO2(g) + O2(g)
The predicted rate law is rate = k[NO][O3]
- Identify the rate determining step.
- Name the reaction intermediate/s. Why is/are it/these intermediate/s?
Define molecularity of reaction.
