Chemical Kinetics — Chemistry STD 12 Science — Question
Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryChemical Kinetics4 Marks
Question
What is reaction intermediate? Explain with an example.
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Answer
Reaction intermediate : The additional species other than the reactants or products formed in the mechanism during progress of the reaction is called reaction intermediate.
Features of reaction intermediate :
The reaction intermediate appears in the reaction mechanism but does not appear in the overall reaction or in the products.
It is always formed in one step and consumed in the subsequent step in the mechanism.
Its concentration is very small and cannot be determined easily.
Rate of the reaction is independent of concentration of this intermediate.
The life period of the reaction intermediate is extremely small, hence cannot be isolated.
The composition of the reaction intermediate, decides the mechanism of the reaction.
Consider decomposition of gaseous $NO _2 Cl .2 NO _2 Cl _{( g )} \rightarrow 2 NO _{2( g )}+ Cl _{2( g )}$
This reaction takes place in two steps: Step I : $NO _2 Cl _{( g )} \xrightarrow{k_1} NO _{2( g )}+ Cl _{( g )}$ (slow, unimolecular) Step II : $NO _2 Cl _{( g )}+ Cl _{( g )} \xrightarrow{k_2} NO _{2( g )}+ Cl _{2( g )}$ (fast, bimolecular) $2 NO _2 Cl _{( g )} \rightarrow 2 NO _{2( g )}+ Cl _{2( g )}$ (overall reaction) $Cl$ formed in Step I is removed in Step II, Hence $Cl$ is a reaction intermediate.
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