Popping popcorn is primarily a physical change rather than a chemical reaction. When the kernel is heated, the moisture inside turns into steam, creating pressure. Eventually, this pressure causes the starch inside the kernel to gelatinize and expand, resulting in the characteristic ‘pop’ and the fluffy texture we associate with popcorn.
While there are some minor chemical changes happening as the heat alters the carbohydrates in the starch, the main process is a physical transition from a hard kernel to a soft popped piece. So, while some chemistry is involved, the act of popping itself does not fit the strict definition of a chemical reaction.