Heating copper wire and sulfur powder In an experiment in school, we heated copper wire (Cu) and yellow sulfur powder together in a crucible. I was wondering why this reaction cannot produce Copper Sulfate. I know it produces Copper Sulfide but I want to know why don't oxygen from the air, sulfur, and copper combine to form copper sulfate.

Can anybody explain this in simple high school terminology?
By burying the copper wire with plenty of sulfur and then heating the mix, the wire becomes completely submerged in liquid sulfur. The liquid sulfur then gets to react with the copper, and any oxygen that could possibly oxidize the copper would have to diffuse into the liquid sulfur before reaching the copper. However, oxygen quickly reacts with heated sulfur forming sulfur oxides, so it never reaches the copper wire. This is all under ideal conditions, of course.

(Originally given as a comment by @Nicolau Saker Neto)