How does chemistry differ from alchemy?

Alchemy was a very early step in understanding chemistry, and set many of the techniques we currently used.

The main difference between chemistry and alchemy are that chemistry is motivated by science, and alchemy is motivated by magical thinking. To put it another way, chemists believe that there is a reproducible and rational explanation for why things happen, whereas alchemists tended to believe that there were certain magical or charmed things that would get the job done for them. It's not that alchemists didn't do any chemistry, or that they didn't accomplish anything - just that they didn't really think the same way as modern scientists do.

OK.

Very good historical presentation on this website: https://www.khanacademy.org/partner-content/big-history-project/stars-and-elements/other-material3/a/from-alchemy-to-chemistry