Question

Any salt ${MCl}_2$ is soluble in water. If the hydration energy should exceed the lattice energy of ${MCl}_2$.

• A. True
• B. False

Answer 1

The correct option is A True

In order to dissolve an ionic solid, water molecules must break up the interactions between all of the ions in the solid. To do this, they orient themselves such that they effectively reduce the localized charge on the ions. This is called hydration.

Hydration of ions is a thermodynamically favorable process, and as such can release heat. This is why it is called the "heat of hydration."

For a salt to be water soluble, it's hydration energy should exceed the lattice energy required to break it into it's constituents.

Hydration energy $>$ lattice energy