Question

What factors determine the value of the enthalpy of hydration?

Answer 1

When an ionic crystal such as NaCl goes into solution, polar water molecules orient themselves around the ions and must overcome the ionic bonds between the Na+ and Cl- ions. Due to the polarity of water molecules, oxygen is slighly negative and hydrogen is slightly positive, the Na+ is attracted to the O in water and Cl- is attracted to the H in water as well. Ionic bonds involves the transfer of electrons from the more electropositive element to the more electronegative element. Covalent bonding formation requires the sharing of electron between two or more elements. How about when a complex ion is formed, what's the nature of bonding between ligands and the ions. Is the complex ion formation in this case an intermediate stage, and that's why energy of dispersion takes into account

Answer 2

This has to do with dissolving compounds in water. it's probably the nature of the bond that determines the enthalpy of formation. ionic compounds completely dissolve in water because they can exist easily as free ions and easily form interactions with water. because this interaction is favorable, i.e. the compound like NaCL likes to exist as Na+ and Cl- there would probably be some energy being released and maybe it would have a negative enthalpy value.

Answer 3

Enthalpy of formation is the change of enthalpy during the formation of 1 mole of compound from its constituents and instead we are dissolving an ionic compound.

Answer 4

We are not forming the ionic compound by uniting its constituents but breaking the ionic bonds.

Answer 5

When water molecules cluster around the ions breaking the ionic bonds, do water molecules fill in the empty orbitals of each ion via coordinate bonds.

Answer 6

yeah, nothing is being formed here. an Ionic bond is being broken, well I guess it's not really a bond per-say because electrons were transferred they are aren't being shared. I would agree with you. My point was that it must be more favorable and energy must be released since it happens spontaneously.

Answer 7

also, I never though of it that way in terms of orbitals, there must be some kind orbital interaction going on

Answer 8

The spontaneity depends on 2 steps, one when a hydrate is formed and the second step is the dispersion of those hydrate ions. As I said earlier, the water molecules orient themselves around each ions, thus forming a hydrate. I am confused about how these water molecules (ligands) are attatched to each ion, is it by filling their empty orbitals. Does the charge on each ion alter after the transfer of electrons. Why is the energy of the dispersion involved even though they are present in solution.

Answer 9

@Kainui

Answer 10

Hydration is the enthalpy change that accompanies the dissolution of one mole of gaseous ions in water. the hydration energy of a metal cation is directly proportional to its polarising power.

Answer 11

Greater the polarising power of cation, greater is the attraction of lone pair of oxygen of water. Hence greater is the extent of hydration & greater is the hydration energy.