Here's a breakdown:

* Acid: Stomach acid is primarily hydrochloric acid (HCl).

* Base: Antacids contain various basic compounds like:

* Calcium carbonate (CaCO3): This is the most common antacid ingredient. It reacts with stomach acid to form calcium chloride (CaCl2), water (H2O), and carbon dioxide (CO2) gas.

* Magnesium hydroxide (Mg(OH)2): This reacts with stomach acid to form magnesium chloride (MgCl2) and water.

* Sodium bicarbonate (NaHCO3): This reacts with stomach acid to form sodium chloride (NaCl), water, and carbon dioxide gas.

Here's a simplified general equation:

Acid + Base → Salt + Water + (Sometimes) Carbon Dioxide

Example with Calcium Carbonate:

2 HCl (acid) + CaCO3 (base) → CaCl2 (salt) + H2O (water) + CO2 (gas)

Why does this relieve heartburn?

The base in antacids neutralizes the excess stomach acid, reducing its acidity and relieving the burning sensation associated with heartburn. The carbon dioxide produced can cause some bloating or burping.

Important Note: Antacids are a temporary solution for heartburn. If you experience frequent or severe heartburn, consult a doctor.