Chemical container returned with speed (7)
I believe the answer is:
nitrate
'chemical' is the definition.
(I've seen this before)
'container returned with speed' is the wordplay.
'container' becomes 'tin' (tin is a kind of container).
'returned' is a reversal indicator.
'with' says to put letters next to each other.
'speed' becomes 'rate' (the speed at which something happens).
'tin' backwards is 'nit'.
'nit'+'rate'='NITRATE'
(Other definitions for nitrate that I've seen before include "following 28 [SILVER]" , "salt" , "Tear tin up for fertiliser" , "Compound" , "Fertiliser chemical" .)