Horace Heffner
Wed, 16 Jul 2008 19:56:50 -0700
On Jul 16, 2008, at 6:33 PM, Robin van Spaandonk wrote:
In reply to Horace Heffner's message of Wed, 16 Jul 2008 14:36:21 -0800:Hi Horace, [snip]When NaCl is dissolved in water the Na+ and Cl- ions are separated by hydration. They each have a polarized layer of water about them that separate them, insulates them, and reduces the force between them, and thus causes the solvation. The energy for this separation comes from the heat of the water.[snip]Not just from the heat of the water. Most of it comes from the binding energy of the ion to the polarized water molecules, of which several surround each ion,and each contributes a small amount. Regards, Robin van Spaandonk <[EMAIL PROTECTED]>
Interesting that the heat of hydration is almost equal to the heat required to break down the crystal lattice. See:
http://www.chem.ox.ac.uk/vrchemistry/energy/Page_25.htmIf the NaCl molecule is returned to solution then the full amount of heat required to break down the crystal lattice is not required again, only the energy needed to break apart a single Na and Cl pair. This means that not as much energy comes from the solvation as I thought, and much of the arc energy ends up back in the water when released by the hydration process. The arc energy and the re- hydration energy should balance out, leaving the possible 2nd Law "excess energy" being that amount which is supplied by the solution to help pull apart the single Na and Cl pair upon subsequent cycles.
Best regards, Horace Heffner http://www.mtaonline.net/~hheffner/