This doesn't seem to be so much a vocabulary issue as it is a grammar issue. These are all grammar points that would appear on a nikyuu JLPT level exam (is that the one you're practicing, or something else?)
わけ reason on its own but is used in many different grammar points in different ways, such that you really can't guess how it will often be used just by knowing the word's most basic meaning.
I'd recommend finding a good intermediate level grammar book; I'm using about four different ones now, and I would recommend An Intermediate Guide to Japanese Grammar in combination with either the 二級日本語能力試験完全マスター文法 or the similar one by Unicom. I liked the latter a bit better.