Torn bags date, revealing chemical substance (7)
I believe the answer is:
reagent
'chemical substance' is the definition.
(I've seen this before)
'torn bags date' is the wordplay.
'torn' becomes 'rent' (rending is a kind of tearing).
'bags' means one lot of letters goes inside another (bag can mean secures or steals).
'date' becomes 'age'.
'rent' enclosing 'age' is 'REAGENT'.
'revealing' acts as a link.
(Other definitions for reagent that I've seen before include "Substance used in chemical analysis" , "will cause some reaction" , "Chemically active substance" , "Reacting substance" , "Get near (anag) - substance used in chemistry" .)