What is the enthalpy for the reaction Ca(OH)2 (s) + CO2 (g) --> CaCO3 (s) + H2O (l)?
Unknown. We would predict it to be negative.
The formation of solid calcium carbonate is a bond forming reaction. A solid precipitate of calcium carbonate occurs. We would thus predict the enthalpy of the reaction to be negative. To give numbers we need experimental data.