unexpended vs leftover

unexpended is not a noun while leftover is a noun.

Word	Noun	Adjective	Verb	Adverb
unexpended	No	Yes	No	No
leftover	Yes	Yes	No	No

As adjectives, unexpended and leftover are synonyms defined as:

Other synonyms of unexpended include left, left over, odd, remaining.

unexpended (noun)	leftover (noun)
	a small part or portion that remains after the main part no longer exists

unexpended (adjective)	leftover (adjective)
not used up	not used up
(of financial resources) not spent