The free energy change of a reaction under non-standard conditions is given by delta-G = delta-G-standard + RT ln(Q), where Q is the reaction quotient built from ion activities (concentration times activity coefficient); the free energy required for dissolution is the negative of the free energy change for the corresponding precipitation reaction.
Standard free energy of precipitation (Ca2+ + CO3^2- -> CaCO3(s)): delta-G-standard = Gf(CaCO3) - Gf(Ca2+) - Gf(CO3^2-) = -1128.94 - (-553.54) - (-527.9) = -47.5...
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