Final answer:
Antacids work by chemically neutralizing stomach acid to provide relief from heartburn and indigestion.
Step-by-step explanation:
Antacids do not require systemic absorption and instead work by chemically neutralizing stomach gastric acid, which reduces damage and provides relief from symptoms such as heartburn and indigestion.
For example, a common antacid like Tums contains calcium carbonate which reacts with hydrochloric acid in the stomach:
CaCO3(s) + 2HCl(aq) -> CaCl2(aq) + H2O(l) + CO2(g)
This reaction not only neutralizes the stomach acid but also produces carbon dioxide gas, which may result in a satisfying belch.