impact vs alter

impact is a noun but alter is not a noun.

Word	Noun	Adjective	Verb	Adverb
impact	Yes	No	Yes	No
alter	No	No	Yes	No

As verbs, alter is a hypernym of impact; that is, alter is a word with a broader meaning than impact:

Other hypernyms of impact include change, modify.

impact (noun)	alter (noun)
influencing strongly
the violent interaction of individuals or groups entering into combat
the striking of one body against another
a forceful consequence; a strong effect

impact (verb)	alter (verb)
have an effect upon	remove the ovaries of
press or wedge together; pack together	become different in some particular way, without permanently losing one's or its former characteristics or essence
	cause to change; make different; cause a transformation
	insert words into texts, often falsifying it thereby
	make an alteration to