Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: ada on March 24, 2015, 09:48:00 PM
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What factors determine the magnitude of the molar enthalpy of solution of an ionic and non-ionic solid?
Please help me!
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Why don't you start by telling us what you think some of them might be. Showing an initial effort is the policy of the forum.
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For ionic compounds would it be the charge on the anion, the atomic radius of the ions, structure of the lattice, solubility of the compound and temperature of solution??
And for non-ionic is it just molecular size and the shape of the compound?
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For ionic compounds would it be the charge on the anion, the atomic radius of the ions, structure of the lattice, solubility of the compound and temperature of solution??
This is a great place to start. The enthalpy of solution is going to be related to how much energy is stored in the lattice (which needs to be broken up to solubilize the resulting ions), and how much energy of attraction (strength of intermolecular interactions) there is between the resulting ions and the molecules of the solvent. Therefore atomic radius of ions, and their effective charge are definitely important. The structure of the lattice is also important, although this itself is dependent on the characteristics of the ions, so it's a little redundant. The compound solubility isn't directly involved. The temperature does make a difference but USUALLY we make an approximation that reaction enthalpies are temperature independent, at least over small temperature ranges.
There's one other thing you forgot: what about the properties of the solvent?
And for non-ionic is it just molecular size and the shape of the compound?
You can basically say the same thing for non-ionic compounds as ionic compounds. Lattic energy is usually a term reserved for ionic solids, but you do still have intermolecular interactions for non-ionic solids, and it takes energy to break these apart to dissolve them. The strength of these interactions, and resulting interactions with solvent molecules, do depend on the size and shape of constituent molecules... but also another important molecular property! Can you think of what it is?
Likewise... what about the properties of the solvent?