Question Statement: Would you expect the enthalpy change of formation of calcium carbonate to be higher or lower than that of magnesium carbonate. What I think: Calcium has a bigger radius than magnesium, hence I expect the lattice energy of MgCO3 to be greater than the CaCO3. I suspect that the enthalpy of formation is related to the lattice energy. But as for how I am not sure. Can anyone enlighten me on this question?