Carbon dioxide is quite soluble in water. And you might also get an acid base reaction of the type:

CO_2 + H_2O \rightarrow HCO_3\ ^- + H^+

This is a fun reaction because it is of great biological importance and is also one we can experience outside of the organs of the body.
In the presence of water, most of the CO2 is just dissolved. Some of it then slowly converts to bicarbonate as Unknown008 shows and, of course, to carbonic acid, H2CO3. Bubbles are deadly in the body so there are enzymes - Carbonic anhydrases - that rapidly convert CO2 into HCO3- and vice versa as required. (Your lungs need CO2 gas to exhale.)
When you open a carbonated beverage there is an initial hiss as CO2 gas escapes. (This fills the gap above the liquid in the bottle.) Then there is a surge of foam as the dissolved CO2 is expelled following the loss of pressure. Then the drink continues to outgas for quite a long time as the H2CO3 slowly breaks down to regenerate the dissolved gas.
When you take the first swig of drink (especially if it is warm) you have an excessive outpouring of gas, It chokes you and can squirt out you nose! This is because of the enzymes in your mouth which almost instantly convert H2CO3 intlo H2O and CO2. Each molecule of enzyme can convert MILLIONS of molecules of H2CO3 every second. WHOOSH!

See how much science there can be in a can of Coke! (Or beer, if you are old enough! ) (Or Champagne, if you are rich enough! )

Lol. :p

Do you know what does Menthos do on fizzy drinks? I never looked up the reaction that could be taking place and your mention of 'excessive outpouring gas' just reminded me of that :rolleyes:

I'm not sure what the reactants are :o

I have heard that the Mentos reaction is due to the nucleation of CO2 bubbles. This is combined with the various ingredients of the drink and candy to maxiize the eruption.
It is pretty spectacular! A couple of years age we demonstrated it after our Organic Chemistry class was finished. It worked great!
Now that you mention it, I remember doing this with M&M candy and cola drinks in the 5th grade (that is 60 years ago). This didn't erupt but it generated a lot of foam that just kept coming and coming. Makes an impressive mess - 5th graders love messes!