unemotionality vs impassiveness

unemotionality and impassiveness both are nouns.

Word	Noun	Adjective	Verb	Adverb
unemotionality	Yes	No	No	No
impassiveness	Yes	No	No	No

As nouns, unemotionality and impassiveness are synonyms defined as:

unemotionality and impassiveness: apathy demonstrated by an absence of emotional reactions

Other synonyms of unemotionality include emotionlessness, impassivity, indifference, phlegm, stolidity.

unemotionality (noun)	impassiveness (noun)
absence of emotion	apathy demonstrated by an absence of emotional reactions
apathy demonstrated by an absence of emotional reactions