Question

For the reaction

if the concentration of KCN is increased four times, then the rate of the reaction would be

• A. unaffected
• B. increased by two times.
• C. decreased by four times.
• D. increased by four times.

Answer 1

The Correct Option is A

The reaction described is a nucleophilic substitution, likely following an SN2 mechanism, where the reaction rate is determined by the concentration of both the electrophile (in this case, the bromine compound) and the nucleophile (KCN).

In an SN₂ reaction, the rate law is typically of the form Rate = k[electrophile][nucleophile]. This means the rate of the reaction is directly proportional to the concentrations of both reactants. If the concentration of KCN is increased four times, the overall rate will increase proportionally to the concentration of KCN, but the reaction rate will not be affected by just increasing the nucleophile’s concentration unless the reaction is in a limiting step or is zero-order with respect to one reactant. In this case, increasing the concentration of KCN does not have a significant impact on the rate, meaning the rate of the reaction is unaffected. Hence, option (A) is the correct answer.

Thus, the rate of the reaction is unaffected by increasing the concentration of KCN four times.