Chemically inactive (5)
I believe the answer is:
inert
'chemically inactive' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for inert that I've seen before include "Incapable of acting, like some gas" , "Sluggish - unresponsive" , "Like e.g. xenon" , "Chemically unreactive" , "Sluggish, inactive" .)