Lathika
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Number of posts : 58
Age : 33
Location : Ernakulam
Job/hobbies : Everything especially sleeping...eating...haa DANCING
Propz :
Registration date : 2009-02-16
 |  Subject: some basics which we dont have ....................... :)  Tue Feb 17, 2009 1:56 pm | |
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- The
RATE LAW for a reaction is a description of the rate of the reaction as it
depends upon the concentrations of various species. It includes a rate
constant, k(small k, not an equilibrium constant, K), which is equal to
the rate of the reaction at unit concentrations of all reagents. As noted
previously, it is a measure of the inherent rate of the reaction,
independent of concentrations.
- A
first order rate law is one which depends upon the concentration of
a single reactant taken to the first power, i.e., the rate is
linearly dependent upon the concentration of that reagent. The order
of the rate law is the sum of the exponents of all concentration
expressions in the rate law.
- The
rate law for the SN1 reaction is first order, depending only
upon the concentration of the alkyl halide, and not at all upon the
concentration of the nucleophile. That is because the first step is the
rate determining one. The subsequent step which involves the
nucleophile is very fast.
- The
"1" of SN1 is the molecularity (the number of
molecules present) of the rate determining step, in which only the alkyl
halide is involved.
- In
contrast, the SN2 reaction is second order, depending
upon the concentrations of both the alkyl halide and the nucleophile, each
linearly. The rate determining step (indeed the only step) is bimolecular,
so that the mechanistic designation is SN2.
- The
reason the rate of this reaction is dependent upon the concentrations of
both reactants is simply that they must collide in order to react.
The number of collisions between the two reagents is directly proportional
to the concentrations of both.
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