Determine how many moles of carbon dioxide (CO2) are formed when 40 g of calcium carbonate (CaCO3) reacts with excess hydrochloric acid (HCl).

To solve this, we use the given chemical equation: CaCO3 + 2HCl → CaCl2 + H2O + CO2. The molar mass of calcium carbonate (CaCO3) is 100 g/mol. The number of moles of calcium carbonate is calculated as follows: n(CaCO3) = m(CaCO3) / M(CaCO3) = 40 g / 100 g/mol = 0.4 mol. From the chemical equation, 1 mol of CaCO3 produces 1 mol of CO2. Therefore, the amount of CO2 formed is 0.4 mol. The answer is 0.4 moles of CO2.