thermochemical equations
2Al s + Fe2O3 s 2Fe s + Al2O3 s + heat to indicate that heat is one of the products. Chemical equations in which heat is shown as either a reactant or a product are called thermochemical equations. In this reaction, the system consists of aluminum, iron, and oxygen atoms; everything else, including the container, makes up the surroundings. During the reaction, so much heat is produced that the iron liquefies. Eventually, the system cools; the iron solidifies as heat is transferred to the surroundings. A process in which heat q is transferred from a system to its surroundings is described as exothermic. By convention, q < 0 for an exothermic reaction.