Match head reaction. High-speed footage of red phosphorus and potassium chlorate being struck with a hammer. This is the reaction that takes place in when striking a match head. The heat generated by the hammer's impact causes a small amount of red phosphorus to be converted to white phosphorus, which ignites spontaneously in air. This triggers the decomposition of potassium chlorate to give oxygen and potassium chloride. The white fumes are phosphorus pentoxide (P4O10).