Differences between order and molecularity:
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Order
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No.
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Molecularity
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It is the sum of powers of the concentrations in the rate law expressions.
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01
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It is the number of molecular of reactants taking part in an elementary reaction or in a rate determining step of a complex reaction.
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Order corresponds to the overall reaction.
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02
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Molecularity is defined for elementary reactions.
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Order might involve one elementary reaction or it might involve a sequence of elementary reactions.
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03
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Molecularity is a part of the whole reaction.
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It is an experimentally determined value.
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04
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It is a theoretical concept.
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It can have fractional value.
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05
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It is always a whole number.
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It can assume zero value.
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06
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It can not have zero value.
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Order of a reaction can change with the conditions such as pressure, temperature, concentration etc.
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07
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Molecularity is invariant for a chemical equation.
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