Is acid rain is a chemical or physical change?

Acid rain's effect on stone is a chemical change. Acid rain can contain hydrochloric acid (HCl), and a stone building can contain calcium carbonate (CaCO3). These two substances react, according to this equation:

2HCl + CaCO3 --> CaCl2 + H2O + CO2

The product calcium chloride (CaCl2) is a salt, and therefore water soluble, so acid rain can literally "eat away" at a stone building, diminishing its aesthetic qualities, and even compromising it structurally over time.