Question

what is difference of Sn2 and Sn1? (Reject the answer that insincere table )

I mean, they are reaction composed with leaving group and nucleophile. I think Sn1 is just detailed version of Sn2.

Sn2 makes two reaction (leaving and substituting) at the same time and Sn1 makes two reaction (substituting after leaving) step by step .....

I dont know why we separate these reactions. please answer me!!!!!! HELP