Using the enthalpy of formation data below, calculate sol H m for CaCl 2 . H f o
ID: 496190 • Letter: U
Question
Using the enthalpy of formation data below, calculate solHm for CaCl2.
Hfo(Ca(aq))= 543.0 kJ mol-1, Hfo(Cl(aq))= 167.080 kJ mol-1, Hfo(CaCl2(s))= 795.8 kJ mol-1
Would you expect solHm of CaCl2 to be the same as that for CaCl2.6H2O? Explain. (Note that this is not a question about measuring solHm, but it asks if solHm will be the same or different for these two substances. If your answer involves heat capacities or temperature differences you are missing the point.)
Explanation / Answer
CaCl2 (s)-------> Ca2+ (aq) + 2Cl(aq)
Hrxn =Hfor(product) - Hfor(reactant)
=( (-543KJ mol^-1 )+(2×(-167.08))) - (-795.8 KJ mol^-1)
= -81.36 KJ/mole
Therefore, Hsoln of CaCl2 is -81.36KJ/mole
Hsoln of CaCl2.6H20 is equal to Hsoln of CaCl2 because 6H20 added is dissociated , so energy is balanced.
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