How does concentration affect SN2 reactions?

Answer 1

Zoe Alexander

Increasing the concentration of either the nucleophile or the substrate increases the reaction rate.

In an #"S"_"N"2# reaction, one bond is broken and another bond is formed at the same time.

Consider the reaction of hydroxide ion with chloromethane.

Both reactants are involved in the transition state, so this is a bimolecular reaction.

The rate law expression is:

r = k[CH₃Br][OH⁻]

This says that the reaction rate is directly proportional to [OH]⁻ and [CH₃Br].

If you increase the concentration of any reactant, the reaction rate will increase.

Increasing the concentration of OH⁻ will increase the rate, because there are more OH⁻ ions attacking the substrate.

Increasing the concentration of CH₃Br will increase the rate, because there are more CH₃Br molecules available to be attacked.

Here's a video on #"S"_"N"2# reactions.

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Answer 2

Madison Anderson

In SN2 (nucleophilic substitution bimolecular) reactions, the rate of reaction is directly proportional to the concentration of both the nucleophile and the substrate. Increasing the concentration of either the nucleophile or the substrate will increase the rate of the reaction. This is because SN2 reactions involve a single step where the nucleophile attacks the substrate from the backside, leading to the formation of a transition state with the nucleophile, the leaving group, and the substrate in close proximity. Higher concentrations increase the likelihood of successful collisions between the nucleophile and the substrate, thereby increasing the reaction rate. However, excessively high concentrations can lead to increased steric hindrance, which may hinder the approach of the nucleophile and slow down the reaction rate.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.