I earned my Ph.D. because I wanted to be a college professor and teach the next generation of chemical engineering students. It was a passion (teaching) I always had and this was a great way to fulfill that dream.
A day in the life of a college professor varies a lot, depending on the day. Most days you will have formal teaching (an undergraduate and/or graduate class) responsibilities and, perhaps, office hours. You will likely spend some time that day preparing for your lecture or lab as well. If you are a research active faculty member (like most are), then you will probably have an individual or group meeting with your research students (both undergraduate and graduate) where they may need guidance or may provide you with an update on their work. You may also spend part of your day editing a journal article you (and your students) are writing or reviewing a paper that has been submitted to a journal. And, of course, you are always answering email!
When you leave for the day (5 or 6 or 7 PM…or later), know that often work is brought home (e.g. writing a proposal to fund your graduate students, preparing or grading an exam, reading and editing the M.S. thesis of a student, etc.) But it is a great job and, in many ways, a labor of love.