Given enough time and dedication you can learn anything on your own. However, physical chemistry is not an easy course - definitely the hardest from a purely conceptual point of view for any chemistry major, and among the hardest among all courses taught at an undergraduate institution. Encountered for the first time, many of the concepts are foreign, bizarre, and even counterintuitive - the principles of QM are different from classical physics, such that there are no analogies in every day life to draw upon (such as particles being in multiple locations at once, the concept of uncertainty, and so on). It's really helpful to have a good teacher who can convey important points, who knows how to test your learning properly, and who can answer questions, because you'll have a billion of them. Of course, it's not a sure thing that you'll have a teacher like this when you enroll for a course, but it also helps when there are other students who are also struggling with the material, because you can work together to gain a group understanding. YMMV of course but if you really want to learn it, you're probably better off taking a course than trying to learn it on your own. At the least, you could audit a course if that sort of thing is allowed at your university.