(chemistry) a chemical reaction

to investigate, to look up, to look into, to study, to examine, to check up on, to look over / (music) to play, to perform (an instrument) / (music) to tune

(pharmacology) reagent

to use / to employ / to make use of, to apply / to spend

chemical reaction / reaction, response / feedback

to react chemically / to respond, to react / be responsive, be sensitive

chemistry (branch of natural science)

chemistry (branch of natural science)

use one thing for many purposes / work someone hard

to use one's head