Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: bidiboom on September 24, 2011, 02:56:27 AM
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Hi guys,
Somewhere in my book, Brown/LeMay/Bursten's Chemistry, it reads:
"... (telling about van der Waals forces and goes on:) Another kind of attractive force, ion-dipole force, is important in solutions. All four forces (3 van der Waals and 1 ion-dipole) are electrostatic in nature, involving attractions between positive and negative species. All tend to be less than 15% as strong as covalent or ionic bonds."
But on the other hand in Solutions chapter I see that NaCl is dissolving in water by the force of ion-dipole forces.. It reads:
"... The ion-dipole attractions between the ions and water molecules are sufficiently strong to pull the ions from their positions in the crystal."
How do you reason this? Would you please share your thoughts?
Thank you..
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1) How many bonds do you break?
2) How many bonds do you form?
3) what is the contribution of entropy?
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The interaction between the water molecule and the ions has compensated the ionic interaction, like 8 or 10 water molecules surrounding one ion. The water molecule network has become more disordered and the entropy hence increases. When you look at this example, you can apply ^G = ^H-T^S and will get a negative value, which means the reaction is feasible.
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Fladermus and Michael, thank you very much.. now I see which perspective I need.. so the approach is this.. ok, thanks a lot, it really helped :)