$$\ce{CO2(g) + Ca^2+(aq) + H2O(aq) <=> CaCO3(s) + 2H^+(aq)}$$
Find the equilibrium constant using a free energy table.
Finding the free energy and plugging it into the equation $\mathrm{G = -RT \ln (\mathit{K})}$ is easy, but I am confused about what $K$ it is. Is it $K_c$ or $K_p$, or does it even matter?
This is important because I am supposed to do equilibrium calculations with it later. I guess I have to use $K_c$, because only the concentrations of the aqueous solutions are given, plus $\ce{CO2}$ is in ppm. I think $\mathrm{G = -RT \ln(\mathit{K})}$ gives me $K_p$, so do I have to convert that into $K_c$ afterwards if I want to do equilibrium calculations?