You have a passing familiarity with chemical reactions and compounds from your upbringing or exposure to someone who worked with chemicals. Maybe you grew up around a family member who was a chemist, or you spent time in an environment where basic chemical knowledge was necessary.
You're not a professional chemist by any means, but you've picked up some basic understanding of how chemicals work and their general properties. Perhaps your parents owned a small lab and you helped out occasionally, or you had enough curiosity to tinker with simple chemical reactions on your own.
As a result of your passing familiarity with chemistry, you have a few Knacks up your sleeve that can come in handy in a variety of situations. You know how to identify different chemicals, for example, or how to create basic chemical reactions.
You still have a ways to go before you are as experienced or knowledgeable as a true professional, but you have started your journey.
Your familiarity with chemistry has trained you to think quickly and respond to unexpected situations. You can attempt any Initiative roll related to reacting to unexpected chemical events with a +1 bonus.
You have picked up tidbits of knowledge of poisons and toxins, including how to create and neutralize them.
You can synthesize medicinal drugs and serums that can heal wounds or provide temporary boosts to physical or mental abilities.
Your familiarity with chemicals can make you overconfident in your abilities. You might attempt experiments or reactions that are beyond your skill level, or fail to recognize the potential dangers of a particular chemical.
While you might have a good grasp of chemical properties, you lack always seem to be misplacing the proper equipment and elements that a true professional would have to hand. This can limit your ability to experiment or analyze chemicals in certain situations.
A little bit of this and a little bit of that; mix it all together and hope you don't go splat. You are willing to take dangerous risks in the name of science.
While not an addiction in the normal sense, you are a hoarder when it comes to chemicals and are always looking to add new substances to your collection.