Surface Area
A nail is placed in a dilute solution of nitric acid.
The iron is oxidized by the nitric acid and the nail slowly dissolved. Click here for a movie.

This is a heterogeneous reaction because the reactants are in different phases. In this case a solid nail is reacting with a liquid solution of nitric acid.

Let's do an experiment to test the effect of surface area on the rate of a heterogeneous chemical reaction.