Effervescence (chemistry)

Effervescence is the escape of gas from an aqueous solution. The term is used to describe the foaming or fizzing that results from a release of gas. An everyday example is seen in carbonated beverages such as soft drinks. The visible bubbles are produced by effervescence from the dissolved gas (which itself is not visible in the liquid solution).

In the lab, a common example of effervescence is seen if hydrochloric acid is added to a block of limestone. If a few pieces of marble or an antacid tablet are put in hydrochloric acid in a test tube fitted with a cork, effervescence of carbon dioxide can be witnessed.

This process is generally represented by the following reaction, where a pressurized dilute solution of carbonic acid in water releases gaseous carbon dioxide at decompression:

$$ \mbox{H}_2\mbox{CO}_3 \longrightarrow \mbox{H}_2\mbox{O} + \mbox{CO}_2$$

In simple terms, it is the result of the chemical reaction occurring in the liquid which produces a gaseous product.