[govibe]

Use the following data to calculate the enthalpy of hydration for calcium chloride and calcium iodide.

               Lattice Energy*   Hsoln
CaCl2(s)   -2247 kJ/mol      -46 kJ/mol
Cal2(s)            -2059 kJ/mol       -104 kJ/mol

*Lattice energy was defined as the energy change for the following process.

M+(g) + X -(g) MX(s)

I know that enthalpy of hydration is delta H2 + delta H3. I know that delta H3 is the lattice energy, but how do I figure out the rest?

[tflint89]

In order to dissolve, lattice energy has to be broken (always endothermic) with the products as gaseous ions and hydration has to occur (exothermic) with the products as aqueous ions. The total enthalpy change is deltaH therefore:

-(lattice enthalpy) + hydration enthalpy = deltaHsol

This simple relationship should give you the answers you require.