The thermite reaction, in which powdered aluminum reacts with copper oxide, is highly exothermic.

Question

2Al(s)+3CuO(s)→Al2O3(s)+3Cu(s)

Use standard enthalpies of formation to find ΔH∘rxn for the thermite reaction.

Answer 1

You have to look up the standard enthalpies of formation for the reactants and products. These can be found either on the internet, or in a reference book. Then the procedure is to sum the ∆Hº_f of the products and subtract from that the sum of the ∆Hº_f of the reactants to get the ∆Hº_f of the reaction. As it turns out, the ∆Hºf of elements (Al and Cu) is zero, so you only need values for Al2O3 and CuO. Look these up and then use

∆Hº_f Al₂O₃ - 3x∆Hº_f CuO to get your answer. Note to multiply the standard value for CuO by three to correct for the stoichiometry of the balanced equation.