There really isn't a difference. There should be, but there isn't. I guess I'd use baked (note spelling) only for a cooking process done in an oven, whereas roasted (note spelling) could be used if the chicken was cooked in an oven, on a grill (a barbecue grill) or on a rotisserie. But if you cook a chicken in an oven, it can be considered either baked or roasted.
Oftentimes the difference between the two just comes down to what's customary. Cake and cookies, for example, are always referred to as baked, whereas potatoes can be either baked or roasted, and the difference is more in what the final dish will look like rather than how the potatoes are cooked.
(Cross-posted with POB, who did what I should have done and looked for previous threads.)
It would be baked chicken or roasted chicken. Both to bake and to roast mean to cook something in an oven. Cakes or bread are normally baked. Chickens are normally roasted. Things which are roasted are normally put in an open dish usually with some sort of fat or oil on top of them. While they cook the meat (it is normally meat but could be vegetables) are usually turned and the fat spooned over (basting).
Yes, baking is done in oven, but roasting could be done on a spit (A skewer which turns over a fire). It also depends on context. Bread is always baked, and the meat served with a traditional sunday lunch is always described as being roasted.
Potatoes are an edge-case. Roasted potatoes and Baked potatoes are very different. Roast potatoes are generally chunks of potato, or very small ones, cooked in fat or spices, whereas a baked potato is generally a whole large potato, sliced and filled with things such as tuna or cheese.
For me, the difference between "baking" and "roasting" has a connection to the cooking temperature. "Roasting" takes place in a hotter oven than does "baking", though this perception is more of a feeling than a rule in my dialect of San Francisco.