Why is the reactivity of all the three classes of alcohols with conc. HCL and ZnCl2 (Lucas reagent) different?

The reaction of alcohols with Lucas reagent (cone. HCL and ZnCl2) follow SN1 mechanism. SN1 mechanism depends upon the stability of carbocations (intermediate). More stable the intermediate carbocation, more reactive is the alcohol.

Tertiary carbocations are most slable among the three classes of carbocations and the order of the stability of carbocation is 3° > 2° > 1°. This order, inturn, reflects the order of reactivity of three classes of alcohols ie., 3° > 2° > 1°

Thus, as the stability of carbocations are different so the reactivity of all the three classes of alcohols with Lucas reagent is different.