Chemistry ocr a level enthalpy

The lattice enthalpy of calcium chloride can be calculated using three of the enthalpy changes below.
Which enthalpy change is not required?


A) enthalpy change of solution of calcium

B)chloride enthalpy change of hydration of CI ions

C)enthalpy change of formation of calcium chloride

D)enthalpy change of hydration of Ca2+ ions

How is it c? Im so stupid sorry

You are not stupid - you are learning. There is a huge difference. There are also several different kinds of Hess cycles you need to know about, so it’s easy to get confused.

When you have enthalpy of solution Hess cycles, you are showing that you can convert the solid ionic compound into aqueous ions either directly, or by decomposing it into gaseous ions (hence you need the lattice enthalpy) and then hydrating the gaseous ions (hence you need the hydration enthalpies of your ions).

Because there is no route in the Hess cycle where the ionic compound is either made from, or broken down to its elements in their standard states, there is no need for the enthalpy of formation.

Okay okay I actually understand that, I think I just got confused bc theres so many diff cycles; might start drawing them all whenever a question pops up to understand/remember them better. Thank you!