The protagonist of neutralization is not the entire glass of liquid

When hydrochloric acid and sodium hydroxide solutions are mixed, the temperature tends to rise. The core particles that really change are the hydrogen ions provided by the acid and the hydroxide ions provided by the base. They combine to form water, and the other ions remain in solution to form salts.

Why does it release heat?

The system releases some energy as the ions rearrange and form more stable water molecules. Concentration, temperature and mixing ratio all affect the thermal effect we actually measure.

Neutralizing reactions in life

Gastric acid and antacids, soil pH adjustment, and acid-base control in sewage treatment all essentially use the same set of ion reaction logic.