When calcium carbonate and hydrochloric acid meet in the stomach, a chemical reaction occurs. The combination of the acid naturally produced by the stomach and the base ingested in the form of calcium carbonate, either through a food source or a mineral supplement, will cause the neutralization of both compounds and the creation of by-products that are neither acidic nor basic. The effect of this combination is a decrease in discomfort due to an excess of stomach acid which can lead to acid reflux or indigestion. In moderation, it is safe for most people to take calcium carbonate to treat excess stomach acid, though there are a few conditions that make taking this mineral inadvisable.
Chemically, the combination of calcium carbonate and hydrochloric acid is a process known as an acid-carbonate reaction. These reactions always cause the atoms of the acid and the carbonate to separate from their original bonds and form new molecular bonds. Once these new bonds are formed, the acid and the carbonate no longer exist, having been transformed into an ionic salt, water, and carbon dioxide.
One of the results of a chemical reaction between calcium carbonate and hydrochloric acid in the stomach is the formation of calcium chloride, which is a type of an ionic salt. Aside from the creation of this salt, the other atoms in the combination, carbon, hydrogen, and oxygen, will combine with each other, forming carbon dioxide and water. While both acids and bases can cause chemical burns, the neutral molecules formed after they react with one another can pass through a person's digestive system without causing the person any harm.
When a person takes a calcium carbonate supplement, the result is often a decrease in the discomfort associated with excess stomach acid. By neutralizing the acid, the calcium carbonate is able to stop or significantly decrease pain from conditions such as acid reflux and indigestion. Though it does not prevent the stomach from releasing additional acid, the use of calcium carbonate is an effective short term solution. In many patients, it may also be advisable to take this supplement in order to increase the amount of calcium in the body or to prevent loss of bone mass. Patients with conditions that include elevated levels of calcium should check with a doctor before using calcium carbonate as a treatment for excessive hydrochloric acid in the stomach.