The thermite reaction is a very exothermic reaction; it has been used to produce liquid iron for welding. A mixture of 2 mol of powdered aluminum metal and 1 mol of iron(III) oxide yields liquid iron and solid aluminum oxide. How many grams of the mixture are needed to produce 360. kJ of heat?

Answer 1

2Al + Fe2O3 ==> 2Fe + Al2O3

You must know the delta H of the reaction. Make sure it is kJ/rxn and not kJ/mol. It takes 27 x 2 = 54 g Al to produce the kJ for delta Hrxn.
54 g Al x (360 kJ/deltaHrxn) = g Al required.
g Fe2O3 required = g Al x (1 mol Fe2O3/2 mol Al) = g Al x (1/2) = g Fe2O3.
g Al + g Fe2O3 = grams of the mixture needed.