Why does Ce2(SO3)3 have a lower solubility than KCl?

Down vote

A saturated solution is at equilibrium (rate of dissolution is equal to rate of crystallization) with some equilibrium constant K1. If you change the temperature of the system at equilibrium, you will observe a different equilibrium constant K2. Whether the equilibrium constant increase or decreases is described by the Van't Hoff equation:

ln(K2K1)=−ΔHR(1T2−1T1)

So it depends on the sign of the enthalpy of reaction, in this case the enthalpy of dissolution.