What is the balanced chemical equation for the reaction used to calculate ΔfH∘ of BaCO3(s) ? If fractional coefficients are required, enter them as a fraction (i.e. 1/3). Indicate the physical states using the abbreviation ( s ), ( l ), or ( g ) for solid, liquid, or gas, respectively. Use ( aq ) for aqueous solution. Express your answer as a chemical equation.