Change of state as floor revolts before speech (11)
I believe the answer is:
evaporation
'change of state' is the definition.
(physical change of state of matter)
'floor revolts before speech' is the wordplay.
'floor' becomes 'pave' (paving is a type of flooring).
'revolts' says the letters should be written backwards.
'before' is a charade indicator (letters next to each other).
'speech' becomes 'oration' (oration is a kind of speech).
'pave' back-to-front is 'evap'.
'evap'+'oration'='EVAPORATION'
'as' is the link.
(Other definitions for evaporation that I've seen before include "Process of a substance changing into vapour" , "One way that water can get into the atmosphere" , "Process of losing moisture" , "Drying" , "The turning of liquid to vapour" .)