What is the balanced chemical equation for the reaction used to calculate ΔH∘fΔHf∘ of CaCO3(s)CaCO3(s)? If fractional coefficients are required, enter them as a fraction (i. e. 1/3). Indicate the physical states using the abbreviation (ss), (ll), or (gg) for solid, liquid, or gas, respectively without indicating allotropes. Use (aqaq) for aqueous solution. Express your answer as a chemical equation.