Gas with person swearing: very unusual scene before church (13)
I believe the answer is:
effervescence
'gas' is the definition.
(gassy bubbles in liquid)
'person swearing very unusual scene before church' is the wordplay.
'person swearing' becomes 'effer' (someone saying the F word).
'very' becomes 'v' (abbreviation).
'unusual' indicates an anagram.
'before' says to put letters next to each other.
'church' becomes 'CE' (abbreviation for Church of England).
'scene' anagrammed gives 'escen'.
'effer'+'v'+'escen'+'ce'='EFFERVESCENCE'
'with' is the link.
(Other definitions for effervescence that I've seen before include "Sparkle" , "Fizziness; vivacity" , "Bubbling - vivacity" , "Frothiness" , "Frothy bubbles" .)