 We want to do a demonstration for the effect of surface area on the rate of the reaction. If I take a solid iron nail and heat it, the reaction with the oxygen in the air is very slow. We're now going to bring in a piece of steel wool, which is basically iron in a very, very finely divided state. We get a very rapid reaction with the oxygen in the air due to the large increase in surface area. We can greatly increase the rate of the reaction by using the steel wool. Instead of having it react with the oxygen in the air, we put it into some pure oxygen. That will increase the concentration of the reactant.