Restless, little devil - one that is into explosive chemical (9)
I believe the answer is:
impatient
'restless' is the definition.
(similar in meaning)
'little devil one that is into explosive chemical' is the wordplay.
'little devil' becomes 'imp' (an imp is a little demon).
'one' becomes 'a' (a thing is one thing).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'into' means one lot of letters goes inside another.
'explosive chemical' becomes 'tnt' (TNT is an example. I am not sure about the 'explosive' bit.).
'ie' put into 'tnt' is 'tient'.
'imp'+'a'+'tient'='IMPATIENT'
Can you help me to learn more?
(Other definitions for impatient that I've seen before include "those who hate waiting" , "Restless or short-tempered" , "Restlessly eager" , "appeared anxious" , "fed up with waiting time?" .)