Reaction rates. Reaction rate increases with concentration of reactants. This effect is demonstrated here using the reaction of chalk (calcium carbonate, CaCO3) with hydrochloric acid (HCl) and sulfuric acid (H2SO4), both 0.2 M molar concentration. Both acids completely dissociate in an aqueous solution. For the same molar concentration, sulfuric acid produces twice as many hydronium ions (H3O+) compared to hydrochloric acid. Carbon dioxide (CO2) bubbles are produced in the respective reactions: CaCO3 + HCl -> CaCl2 + H2O + CO2 and CaCO3 + H2SO4 -> CaSO4 + H2O + CO2. The reaction is visibly more vigorous (higher reaction rate) in the right beaker (sulfuric acid) than in left beaker (hydrochloric acid).