The enthalpies of formation of nesquehonite, MgCO3 * 3H2O, and hydromagnesite, 5MgO * 4CO2 * 5H2O

The enthalpies of formation, ΔH°_f, of nesquehonite, MgCO₃ * 3H₂O, and hydromagnesite, 5MgO * 4CO₂ * 5H₂O, have been determined by HCl solution calorimetry. For the reaction MgO(c) + CO₂(g) + 3H₂O(l) = MgCO₂ * 3H₂O(c), the enthalpy change at 298.15 K is -29,781*40 cal mor' . For the reaction 5MgO(c) + 4CO₂ + 5H₂O = 5MgO * 4CO₂ * 5H₂O, the enthalpy change at 298.15 K is -120,310±120 cal. For MgCO₃ * 3H₂O the standard molar enthalpy and standard Gibbs free energy of formation, ΔH°_f,298 and ΔG°_f,298 are -472,576+110 and 412,040±120 cal. ΔH°_f,298 and ΔG°_f,298 for 5MgO * 4CO₂ * 5H₂O are -1,557,090±250 and -1,401,71 0±250 cal.