One of the best science mods

Alchemistry is one of my favorite mods. If you like chemistry like me, then this mod is loads of fun. On its own it doesn't do much, but in a modpack can be configured for all sorts of custom progression and research. The default conversions/ recipes are a little OP in some cases, but with some adjustment (like drastically increasing the amount of chemical needed to craft something, and some recipe edits, because being able to craft thousands of ingots from a small vegetable farm is a little.... ya) this totally fits into a pack that is heavy on science and material synthesis.
The best part is, it's 100% configurable. If you don't need a specific element or compound, you can just remove it. And my favorite part is that you can add your own compounds and elements, so you can add just the compounds you need, or even create fictional elements and compounds to fit your pack (a bit of a time consuming pain to create ones that would realistically work and chemically make sense at least a little, but that just makes it all the more awesome).