classroom vs study hall

classroom and study hall both are nouns.

Word	Noun	Adjective	Verb	Adverb
classroom	Yes	No	No	No
study hall	Yes	No	No	No

As nouns, study hall is a hyponym of classroom; that is, study hall is a word with a more specific, narrower meaning than classroom:

Other hyponyms of classroom include home room, homeroom, lecture room.

classroom (noun)	study hall (noun)
a room in a school where lessons take place	a classroom reserved for study
	a period of time during the school day that is set aside for study