When hydrochloric acid (chemical formula: HCl) reacts with sodium carbonate (chemical formula: Na2CO3), one of two reactions will take place, depending on the relative quantities of each chemical.

If hydrochloric acid is in excess quantity, the following reaction will take place:

`Na_2CO_3 + 2HCl -> 2NaCl + H_2O + CO_2`

In this reaction, sodium carbonate reacts with excess hydrochloric acid to form sodium chloride, water and carbon dioxide. In this reaction, bubbles of carbon dioxide are observed.

If hydrochloric acid is not in excess amount, the reaction will be:

`Na_2CO_3 + HCl -> NaHCO_3 + NaCl`

In this reaction, sodium carbonate reacts with hydrochloric acid to form sodium bicarbonate and sodium chloride. No gas is formed in this and hence bubble formation will not be observed.

Thus, the chemical reaction will depend on the amount of each of the reacting species.

Hope this helps.