Final answer:
The main difference between SN1 and SN2 reactions is the reaction mechanism and the rate-determining step.
Step-by-step explanation:
The main difference between SN1 and SN2 reactions is the reaction mechanism and the rate-determining step. In an SN1 reaction, the reaction occurs in two steps: the formation of a carbocation intermediate and the attack of a nucleophile on the intermediate.
The rate-determining step is the formation of the carbocation. In an SN2 reaction, the reaction occurs in a single step where the nucleophile attacks the substrate at the same time the leaving group leaves. The rate-determining step is the collision between the nucleophile and the substrate.