This problem demands a fairly deep understanding of thermodynamic relationships.
The universe in this problem is but the system and the surroundings.
CaO(s) + H_2O(l) rightleftharpoons Ca(OH)_2(s)
Consider,
DeltaS_("univ") = DeltaS_("sys") + DeltaS_("surr"),
The change in enthalpy or entropy of a system is the sum of the property for products less the sum of the property for reactants,
DeltaS = (DeltaH)/T, and,
-DeltaH_("sys") = DeltaH_("surr")
=> -(DeltaH_("sys"))/T = (DeltaH_("surr"))/T
=> DeltaS_("surr") = -(DeltaH_("sys"))/T
Hence,
DeltaH_("sys") = -65.2kJ
therefore DeltaH_("surr") = 65.2kJ, and DeltaS_"surr" = (6.52*10^4J)/(298K) approx (218.7J)/K
Moreover,
DeltaS_"sys" = (-26.4J)/K
DeltaS_("univ") = DeltaS_"surr" + DeltaS_"sys" approx (192.3J)/K
I'm open to feedback if I made a mistake!
