Is an antacid medicaine reacting with stomach acid example of a physical rather than chemical change?

No, the reaction between an antacid medicine and stomach acid is an example of a chemical change.

A physical change is a change in the form or appearance of a substance without a change in its chemical composition. For example, melting ice is a physical change because the water molecules are still H2O, just in a different state (solid to liquid).

A chemical change is a change in the chemical composition of a substance, resulting in the formation of one or more new substances. For example, burning wood is a chemical change because the wood reacts with oxygen to form new substances such as carbon dioxide and water.

In the case of an antacid medicine reacting with stomach acid, the antacid medicine (usually a base such as sodium bicarbonate) reacts with the stomach acid (usually hydrochloric acid) to form new substances such as water, carbon dioxide, and sodium chloride. This is a chemical change because the starting materials (antacid medicine and stomach acid) are different from the products (water, carbon dioxide, and sodium chloride).