How do you know if an acid-metal reaction forms water and CO2 or carbonic acid?

[pivoxa15]

When doing reactions of acid and metal compound, How do you know whether (one water and carbondioxide) or one carbonic acid will be formed? Since they have the same number of elements in the same proportion.

 

[PPonte]

Actually, one carbonic acid decomposes in one molecule of water and one molecule of carbon dioxide. Therefore, when doing chemical reactions you may right one carbonic acid or one molecule of water and one molecule of carbon dioxide, since both ways are correct.

 

[3trQN]

A reaction occurs because the resulting compound is more stable in some way, usually the main reaction product varies with varying conditions, pressure & temperature, pH etc. Also, there is rarley a clear cut line distinguishing the point at which one product is formed from another, it is a dynamic relationship or a equillibrium between reaction products.

Carefully setting up the reaction conditions to favour the maximum yield of product is what its about i guess.

With the example you gave i think it can be inferred from the fact that one of the products ( carbonic acid ) is the soluble form of carbon dioxide, and that as the pressure of the reaction conditions is raised, the equillibrium point of the reaction will shift away from the formation of the gas.

Also i believe that some products will hinder the yield by shifting the equillibrium point away from the optimum, as more CO2 is formed (in a closed system) the pressure would increase and hence the equillibrium point would eventually shift.

Maybe someone can give a better explanation this, or at least a more mathematical one :P