Animation of a large chunk of calcium carbonate being attacked by hydrochloric acid. This is part of a demonstration showing the effect of the surface area of the reactants on the rate of a chemical reaction. The surface of the chunk is exposed to the acid, which reacts to produce carbon dioxide gas, which bubbles off (top), and also water, and calcium and chloride ions. As the ions enter the solution, more of the fresh calcium carbonate is exposed to the acid, so the chunk is eaten away. As the surface has to be eroded before more acid can attack the deeper layers, the surface area to volume ratio of the calcium carbonate determines how quickly the reaction proceeds. The same reaction with several small chunks is seen in K005/0344.