There's nothing especially wrong with querying two projects at once, but most agents want to represent YOU, not just one book. If your other book is in a genre they don't represent they will normally find a way around it, but that would be case-by-case. They might decide to rep it anyhow, they might get another agent to rep it who they know, or who works with them, or they might give you the option of finding someone on your own for that book.
However, that said, I really don't think you get how much work it is to find an agent. If you've never been agented before, to suddenly have two books, both with offers.... Well it's probably not unprecedented, but let's just say it's highly unlikely.