When we "intellectualize," what we're really doing is conceptualizing, as objectively as we can. We are trying to locate a source for our knowledge (through a process that involves "epistemology," looking for the difference between belief and opinion). Using epistemology as a way to think and conceptualize, we come to know a thing. As we intellectualize, and put things into perspective (using critical thinking skills) we begin to "rationalize," or find the rationale for, something we have 1) conceptualized 2) understood the meaning of (for ourselves) and 3) begun to fully understand and determine a reason for its being.
Intellectualizing requires being able to think abstractly about a subject. Rationalizing about it requires being able to understand what you have imagined or understood objectively and abstractly. These words I am typing will form an idea in your mind. Intellectually, you will understand what I'm saying, since I'm writing in fairly clear English; rationalizing them, in other words, explaining their meaning to yourself, might prove a little harder, especially if you don't look up the word "epistemology." ;-)
In trying to state it as simply as possible, when we intellectualize we are actually ignoring the emotional or psychological significance of an action or situation by creating an abstract explanation for it. We are taking the "humanity" out of the situation.
When a person rationalizes a situation he is basing an action, feeling, etc., totally on reason.