The fizzing that occurs when sodium hydrogen carbonate (NaHCO3) is added to sulfuric acid (H2SO4) is due to a chemical reaction that produces carbon dioxide gas (CO2), water (H2O), and sodium sulfate (Na2SO4). The balanced chemical equation for this reaction is:
NaHCO3 + H2SO4 → Na2SO4 + CO2 + H2O
The fizzing occurs as the carbon dioxide gas is produced and released from the mixture.
The fizzing is fastest immediately after the NaHCO3 is added because at that moment, the surface area of the NaHCO3 particles is at its highest. This increased surface area provides more sites for the acid to react with, resulting in a greater number of reactions occurring simultaneously and a faster production of CO2 gas. As the reaction progresses, the surface area of the remaining NaHCO3 particles decreases, slowing down the rate of reaction and the production of CO2 gas.