I got a Chihuahua puppy 2 weeks ago. He is now 8 weeks old. Currently I can leave him alone for roughly 2hours and he is fine the whole time. I am at home all day every day at the moment but I'm starting a Course next week 1 day a week for 10weeks. I will have to be away from 9am to 2:30pm

He is already crate trained and has a play pen that I can attach to his crate whilst I'm out in case he wakes up and wants the bathroom or to play. Will I be able to leave my puppy for this long?

Is his crate/play pen inside the house or outside? If it is inside, as long as he has water, food and a place to go potty and lay down I don't see it being a problem. If its outside, it depends on where you live, and how hot it gets.

Its all inside- my living room to be precise. He has his bed food and water inside his crate with him and all of his toys in the play pen.
I just hope he doesn't get too lonely. I do have an older dog that wanders freely around the house so he will have the odd bit of company too.

Five and a half hours one day a week should be fine. He might have an accident the first couple of times, but as he gets older he will be able to hold it longer. Always check the toys carefully, making sure if they are damaged to remove them immediately. Your baby will most likely sleep most of the time you are gone. Congratulations on your new family member!