Question

if 21.54 grams of caco3 is added to an ecxess of HCl in the equation Cacl3+2Hcl produces Cacl3+co2+H20, what mass does co2 produce?

Answer 1

You have two typos in your equation. The correct equation, balanced, is

CaCO3 + 2HCl ==> CaCl2 + H2O + CO2
mols CaCO3 = grams/molar mass
mols CO2 = mols CaCO3 from the coefficients in the balanced equation.
Now g CO2 = mols CO2 x molar mass CO2.