Response after series showing chemical process (5,8)
I believe the answer is:
chain reaction
'chemical process' is the definition.
(chain reaction is a kind of chemical process)
'response after series' is the wordplay.
'response' becomes 'reaction' (synonyms).
'after' is a charade indicator (letters next to each other).
'series' becomes 'chain' (chain is a kind of series).
'reaction' after 'chain' is 'CHAIN REACTION'.
'showing' acts as a link.
(Other definitions for chain reaction that I've seen before include "This process should continue" , "Continuing process" , "Series of consequences" , "Series of stimulated responses" , "Sequence" .)