I think if I were a teacher and entered the classroom, the liveliness of the students' chatter would turn to silence.
この場合、次のような言い方ができますよ。
ーI think if I were a teacher and entered the classroom, the liveliness of the students' chatter would turn to silence.
「もし私が教師で、教室に入ったら、生徒たちのお喋りの賑やかさが静寂に変わると思う」
liveliness で「活気・賑やかさ」
to trun to silence で「静寂に変わる」
ご参考まで!