ending vs change of state

ending and change of state both are nouns.

Word	Noun	Adjective	Verb	Adverb
ending	Yes	No	No	No
change of state	Yes	No	No	No

As nouns, change of state is a hypernym of ending; that is, change of state is a word with a broader meaning than ending:

ending: the act of ending something
change of state: the act of changing something into something different in essential characteristics

ending (noun)	change of state (noun)
the act of ending something	the act of changing something into something different in essential characteristics
the end of a word (a suffix or inflectional ending or final morpheme)
the last section of a communication
event whose occurrence ends something
the point in time at which something ends