* Physical Change: A physical change alters the form or appearance of a substance but doesn't change its chemical composition.

* Chemical Reaction: A chemical reaction involves the formation of new substances with different chemical properties.

In carbonation:

* CO2 gas is dissolved in water. This is a physical process of dissolving, where the CO2 molecules are simply dispersed within the water molecules.

* The dissolved CO2 forms carbonic acid (H2CO3). This is a chemical reaction, but it's a reversible reaction that happens quickly and is easily reversed.

* The carbonic acid gives the fizzy sensation and tart taste. This is a result of the physical properties of the dissolved gas and the acid.

Key Point: While there is a chemical reaction involved in the formation of carbonic acid, the overall process of carbonation is primarily driven by the physical process of dissolving CO2 in water. This doesn't change the fundamental chemical composition of the water or the CO2.