accidentally vs unexpectedly

accidentally and unexpectedly both are adverbs.

Word	Noun	Adjective	Verb	Adverb
accidentally	No	No	No	Yes
unexpectedly	No	No	No	Yes

As adverbs, accidentally and unexpectedly are synonyms defined as:

Other synonyms of accidentally include by chance, circumstantially.

accidentally (adverb)	unexpectedly (adverb)
without advance planning	without advance planning
without intention; in an unintentional manner	in a way that was not expected
of a minor or subordinate nature