[...] a theoretical value [...]
I don't believe the heat of formation of the varied hydrates can be predicted. I depends on every detail of the crystal arrangement. Worse, the heat of dissolution is small as compared with the heat of formation of the compounds, hence its relative uncertainty is huge.
I wouldn't even assume a linear relationship from the anhydrous solid, a solid with few H2
O, with 10 H2
O, and a solution. Most salts show a finite set of combinations with crystallisation H2
O, which tells that geometrical details are all-important. This would be an interesting observation to make and to comment from your experiment. Or even: start from 10 H2
O, use scales to evaporate 1 H2
O at a time as a mean value (the solid will be a mix of varied crystals), measure each time the heat of dissolution, and attribute breaks in the curve to favoured numbers of crystallisation water.
Software would be far too inaccurate here.
The only "prediction" I imagine is to find experimental values for each hydration number. Passing numerically between the heats of formation and dissolution isn't a big deal then. I'd prefer measured heats of dissolution, because uncertainties on the heat of formation make a huge relative difference on the heat of dissolution.