Workers who build railway tracks often use a process called thermite welding to connect pieces of track. Thermite is a mixture of aluminum metal (Al) and ferric oxide (Fe2O3). A worker places thermite between two pieces of track and then burns it to form aluminum oxide (Al2O3) and iron (Fe). As the reaction happens, the air around the mixture becomes so hot that the two pieces of track fuse together. Is this chemical exothermic or endothermic?