Hey Trevor! When it comes to predicting products of reactions we are usually giving the major products, but always keep in mind that minor products are still possible. Our understanding of chemistry is constantly expanding - I try to keep the content relevant to the majority of courses but always recommend you listen to your own professor as they will be grading your tests! Happy studying :)
The ZnCl2 is needed for both SN1 and SN2. The combination of HCl/ZnCl2 is actually referred to as the Lucas reagent and can be used to classify alcohols as primary, secondary, and tertiary. The tertiary alcohols react the fastest followed by the secondary (both reacting by SN1). The primary alcohols react the slowest (by SN2), and the time for the reaction to occur allows for the determination. Hope this helps!