Gas, more than enough? That’s too much! (6)
I believe the answer is:
ethane
'gas' is the definition.
(ethane is a gas)
'more than enough? that's too much' is the wordplay.
'that's too much' says the answer is hidden in the clue (the clue hides the answer plus unneeded letters).
'ETHANE' is hidden in the letters of 'more than enough'.
(Other definitions for ethane that I've seen before include "Flammable hydrocarbon" , "Compound" , "Ate hen (anag) - hydrocarbon gas" , "Athene (anag.); a colourless gas" , "Chemical" .)