Chemical Weathering

"Rocks can be broken down by chemical weathering."

Here are two examples. Find a limestone rock. These are usually found in driveways. Put the rock in a glass with vinegar. Did it start bubbling right away? The lime in the rock reacts with the acid in the vinegar and the bubbles coming off are carbon dioxide which formed during the chemical reaction. Let it sit overnight. You might find sediments in the cup in the morning. These sediments are from the rock. If you don't get a reaction from the rock, you can use a piece of chalk. It will bubble right away, and break down. Chalk is just a softer type of limestone, although sometimes chalk is made of another type of mineral called gypsum (calcium sulfate.)

Put some steel wool in a cup of vinegar as well.

How does it change over time? What do you see floating in the vinegar? Steel wool has iron in it, which rusts. The red color is the rust.

Acid in rain is like the acid in the vinegar and results in chemical weathering. The acid in rain is less acidic than the vinegar, however, so will take longer than overnight.

So, what is the difference between physical weathering and chemical weathering? In physical weathering the composition of the rock stays the same, but the size of the rock changes as the rock goes from large rocks to smaller pieces in the process of the physical weathering. In chemical weathering the composition of the rock changes due to a reaction with some chemical, usually an acid.

source: Exploring Creation with General Science, Jay Wile