why isn't it possible to directly measure enthalpy change for conversion of the blue hydrated copper sulfate crystals to white anhydrous crystals
For that to happen, you have to heat up the hydrated crystals so that the water evaporates away. As you are heating it up yourself, you can't measure the temperature change from the reaction itself.
dehydration reaction can not be controlled temp change of dehydration cannot be measured hydrated copper sulphate would need heating ( so cant measure temp change) impossible to add exact amount of water- to get value for reverse process cant mix solid with water to get perfect crystals.
For that to happen, you have to heat up the hydrated crystals so that the water evaporates away. As you are heating it up yourself, you can't measure the temperature change from the reaction itself.
dehydration reaction can not be controlled temp change of dehydration cannot be measured hydrated copper sulphate would need heating ( so cant measure temp change) impossible to add exact amount of water- to get value for reverse process cant mix solid with water to get perfect crystals.