The problem isn't the word 'exposed' per se: the problem is that there's something missing from your sentence. The word 'exposed' on its own is meaningless. Exposed to what? The students need to have been exposed TO something. You could say, for example: Talking about this subject after being exposed to the relevant vocabulary helps students have better ideas about the topic.

Su.Ki. is right. It looks like your sentence is missing something to explain what you mean by "being exposed." To "expose something" is to reveal it or display it. We usually use the word "expose" to describe revealing something that was hidden or secret. If you use the passive voice to say that a person has "been exposed," it usually means either: a) the person did something and tried to keep it a secret, but the secret has now been revealed or b) the person's clothing has been removed (his/her naked body is "exposed" or revealed) If you say that someone has been "exposed to" something, this means that the person has experienced, endured, or learned about something. This seems like the meaning you intend, but as Su.Ki. says, you need to explain what you're saying the students were exposed to. Is it "breakfast"? Are you saying that students should talk about breakfast after they eat breakfast?