Have you ever noticed how the inscriptions on some old tombstones are difficult to read? Weathering causes this problem. Weathering takes place through physical and chemical processes. Physical weathering, a process in which rocks are physically changed, results from abrasion, wetting and drying, freezing and thawing, expansion and contraction, crystallization of minerals, action of organisms, and the growth of plant roots. All of these processes help to break rocks into fragments. Once rocks have undergone physical weathering, they are especially vulnerable to chemical weathering, a process in which the original minerals in rocks change into other substances. A rock that is broken into fragments has more surface area, and therefore more regions that are exposed to chemicals, than a solid rock. In this experiment, you will find out how the surface area of a material affects the rate of chemical weathering.
Rocks and minerals can be worn down over a period by physical weathering. Several physical processes accelerate weathering of rocks and minerals by splitting them into fragments. For example, when water freezes in the cracks and crevices of a rock, it expands, pushing the rock segments apart. The roots of plants can have a similar effect. Since chemical reactions can only occur at the places where solid materials come in contact with liquids or gases, breaking a solid material apart increases the area where interaction can occur. To understand how this works, think about making a peanut butter sandwich from a loaf of bread. If the loaf of bread is not sliced, you can only spread peanut butter on outer surfaces. By cutting a slice of bread, you create a new surface area on which you can spread peanut butter. Each additional slice provides more surface area. In the same way, each "slice" of rock is exposed to chemical interactions.