[INDENT] A [INDENT] B
H2O + CO2 -> H2CO3 -> H+ + HCO3-

What kind of reaction is A and what does rxn B tell you about what kind of molecule HCO3 - is?

I know rxn a is a synthesis rxn... the combination of water and carbon dioxide to form this new compound... at least I am pretty sure.
Rxn B is where I am puzzled. I think that some outside element, maybe heat, is added to H2CO3 in order to separate it into its respective hydrogen ion and HCO3 - ion. Am I way off?

I think that can be called a synthesis reaction.

The B reaction, is not due to heat. The molecule H2CO3 is in water, do you agree. Well, in water, the molecule does not remain like its molecular formula suggests but is in the form of molecules.

If you want to know why, the water acts like a solvent. Water has slightly charged ends and can separate the H2CO3 into the H+ and HCO3- ions.

CO2 + H2O ⇌ H2CO3 Carbonic acid, a weak diprotic acid which disassociates stepwise according to the equilibrium statements:

H2CO3 ⇌ HCO3− + H+ Ka = 2.5×10−4

HCO3− ⇌ CO32− + H+ Ka = 5.61×10−11

The overall reaction can be written as:

CO2 + H2O ⇌ HCO3− + H+ Ka = 4.30×10−7

Notice the sizable negative exponent in the equilibrium constant above. This means the reaction favors the reactants and the solution to a large extent exists as mostly CO2 and water. Its an acid-base reaction and a buffer solution.

Its important as a blood buffer.