The chemical equation for the reaction of magnesium bicarbonate and citric acid is:

$$3Mg(HCO_3)_2 + 2C_6H_8O_7 → Mg_3(C_6H_5O_7)_2 + 6CO_2 + 3H_2O$$

In this reaction, magnesium bicarbonate (Mg(HCO3)2) and citric acid (C6H8O7) react to form magnesium citrate (Mg3(C6H5O7)2), carbon dioxide (CO2), and water (H2O).