A hand-warmer purchased by campers and skiers consists of a sealed outer plastic bag and an inner perforated plastic bag containing powdered iron, water, salt and sawdust. When the inner bag is taken out and shaken it becomes hot because the following reaction occurs:
4Fe(s) + 3O2(g) ® 2Fe2O3(s); DH = -823 kJ mol-1
The bag contains 15.0 g of iron that reacts completely.
Calculate the energy released by the hand-warmer.