Difference between order and molecularity
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The main difference between the order of a reaction and molecularity of a reaction are given below:
ORDER OF A REACTION
1. It is 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.
2. It need not be a whole number i.e. it can be fractional as well as zero.
3. It can be determined experimentally only and cannot be calculated.
4. It is for the overall reaction and no separate steps are written to obtain it.
5. Even the order of a simple reaction may not be equal to the number of molecules of the reactants as seen from the unbalance equation.
MOLECULARITY OF A REACTION
1. It is the number of atoms, ions or molecules that must collide with one another simultaneously so as to result into a chemical reaction.
2. It is always a whole number.
3. It can be calculated by simply adding the molecules of the slowest step.
4. The overall molecularity of a complex reaction has no significance. It is only slowest step whose molecularity has significance for the overall reaction.
5. For simple reactions, the molecularity can usually be obtained from the Stoichiometry of the equation.
ORDER OF A REACTION
1. It is 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.
2. It need not be a whole number i.e. it can be fractional as well as zero.
3. It can be determined experimentally only and cannot be calculated.
4. It is for the overall reaction and no separate steps are written to obtain it.
5. Even the order of a simple reaction may not be equal to the number of molecules of the reactants as seen from the unbalance equation.
MOLECULARITY OF A REACTION
1. It is the number of atoms, ions or molecules that must collide with one another simultaneously so as to result into a chemical reaction.
2. It is always a whole number.
3. It can be calculated by simply adding the molecules of the slowest step.
4. The overall molecularity of a complex reaction has no significance. It is only slowest step whose molecularity has significance for the overall reaction.
5. For simple reactions, the molecularity can usually be obtained from the Stoichiometry of the equation.
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ORDER AND MOLECULARITY
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ORDER
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=> the sum of the powers of the concentration terms in rate law expression
=> it is determined experimentally
=> it can be a whole number, zero or even fraction
=> provides some ideas about. Reaction mechanism
MOLECULARITY
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=> it is the number of reacting species undergoing simultaneous collision in the reaction
=> it is a theoretical concept
=> it always a whole number
=> does not tell us the reaction mechanism
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