The reaction in baking soda and vinegar rockets is an acid/base reaction in between the sodium bicarbonate (NaHCO₃) of the baking soda and the acetic acid (CH₃COOH) in the vinegar. The sodium bicarbonate reacts with hydrogen protons (H+) to sodium ions (Na+), carbon dioxide (CO₂), and water (H₂O):
NaHCO₃ + H+ -> Na+ + CO₂ + H₂O
The acetic acid can dissociate in water:
CH₃COOH <-> CH₃COO- + H+
The combined reaction of mixing both is therefore:
NaHCO₃ + CH₃COOH -> CH₃COONa + H₂O + CO₂

In this reaction, the sodium ion (Na+) reacts with the acetate anion (CH₃COO-) to sodium acetate (CH₃COONa). This reaction can be called a double-replacement reaction, since two parts of two ionic compounds are exchanged (Na+ and H+) and this exchange forms two new compounds:
CH₃COONa + H₂O. The valence electrons play an important role in this reaction. A Lewis acid is a compound that can accept valence electrons (typically has a positive charge) and a Lewis base is a compound that can donate a pair of valence electrons. If the two react, they can form a covalent bond and share the two electrons of the Lewis base. In our case, the acetic acid dissociates in water to a Lewis base (CH₃COO-) and a Lewis acid (H+). The hydrogen proton is now looking for a Lewis base that it can react with to obtain one valence electron. It reacts with sodium bicarbonate as described above and another Lewis acid, the Na+ ion, is released. This ion is now reacting with the other available Lewis base CH₃COO- to form CH₃COONa.

The ratio of vinegar to baking soda is important for the reaction that happens in the liquid phase. In order for this reaction to happen fast, the vinegar should be able to dissolve the baking soda quickly and foster a fast reaction. Therefore, more vinegar is better. A ratio of 12 to 1 of vinegar to baking soda is proven to be effective. Since the rocket is only sealed off by a cork, the pressure building up is limited and a function of the reaction speed - a faster reaction means more pressure and a more successful rocket. However, too much vinegar and baking soda will make the rocket too heavy to fly to a sufficient height. The issue here is the amount of pressure the cork can withstand before the rocket takes off. Additionally, a bottle with a larger volume will increase the air resistance and slow the rocket down. A smaller bottle combined with a strong and snug sitting cork will give the best result.