When bread is made does the chemical change form a gas?

Making bread involves a step called leavening (usually), and that's the part of the operation where your question regarding bread making chemistry is pointing. A leavening agent causes gas to be produced. Be sure to read enough to differentiate the effect of steam (created inside the dough mass) on the finished bread from leavening. Point your cursor to the link and surf on over to our friends at Wikipedia to get the straight scoop. These folks are down with it.