serenity vs peace of mind

serenity and peace of mind both are nouns.

Word	Noun	Adjective	Verb	Adverb
serenity	Yes	No	No	No
peace of mind	Yes	No	No	No

As nouns, serenity and peace of mind are synonyms defined as:

Other synonyms of serenity include ataraxis, heartsease, peace, peacefulness, repose.

serenity (noun)	peace of mind (noun)
a disposition free from stress or emotion	the absence of mental stress or anxiety
the absence of mental stress or anxiety