Wikipedia:Reference desk/Archives/Science/2018 November 28

= November 28 =

Chemical potential
I have had some trouble applying our article on chemical potential or similar sources to actually figure the amount of energy in a chemical potential. For example, in the section on deviation from ideality, the chemical potential is said to depend on ln(x), where x is the mol fraction of solute, yet the graph depicts it intersecting with the y axis. So to be clear, suppose great alien overlords hand me a liter of absolutely pure water at STP, and in a mad act of defiance I add x moles of NaCl to it, perhaps hoping for an infinitely large explosion. What's the real formula and/or data for the amount of energy released? Wnt (talk) 14:35, 28 November 2018 (UTC)


 * Have you read our article, Enthalpy change of solution? Nimur (talk) 15:33, 28 November 2018 (UTC)
 * Per Nimur, the enthalpy change of solution is really what you are looking for. The chemical potential concept is really a generalized measure of free energy, and is a fairly esoteric way to get at the energy changes of a reaction.  Specific enthalpy relations are usually much more useful, such as enthalpy of reaction, enthalpy of solution, etc.  -- Jayron 32 16:24, 28 November 2018 (UTC)


 * Well, the problem with the enthalpy change of solution article is that it applies only at infinite dilution (or in that approximation). I mean yes, it says the energy released isn't infinite, but I still don't know how to go from a concentration difference to energy release.  I was reminded of this issue by the question above about ion excretion:  I wanted to say "you can't purify all the copper out of your urine, because it takes a lot of energy to do that" but I don't actually know that's true.  I mean, chemical potential runs the mitochondrial ATP production and costs of desalination and countless other things, and I don't have a grip on how to do the math about it. Wnt (talk) 12:51, 29 November 2018 (UTC)
 * It's calculated from a partial differential equation of energy with respect to number of particles. Which energy term you use (and which variables are left to float) are based on which application you want.  The article on chemical potential has the equations for calculating it with respect to internal energy, enthalpy, Gibbs free energy, or Helmholtz free energy.  At this point, you've exhausted my calculus knowledge, and if you've exhausted your own, I'm not sure what else to do.  The reason it's so messy is that chemical potential is basically potential energy between the different particles in a system, and depends solely on 1) the average strength of one of those interactions and 2) the number of those particles, and of course it varies nonlinearly (that is a 4 particle system does not have a value double that of a 2 particle system), and also varies with respect to other factors like temperature, pressure, etc.  and ALSO we're not dealing with 2 or 4 particles, but things on the scale of Avogadro's number of particles.
 * Chemical potential calculations are not usually done from first principles to produce direct single numerical calculations. Usually, you do that calculus to derive a specific equation that would be applicable to your system, and then simplify or approximate the equation to get something close enough for your purposes (i.e. the Ideal Gas Law, the Enthalpy of solution, the specific heat equations can, IIRC, all be derived from first principles starting at Chemical Potential.  At least, I remember having to do stuff like that when I took physical chemistry, back in 1996-1997, and I'm pretty sure I forgot it by about 1998.  The point I'm trying to make is, you can do it, but you probably don't want to because someone already did the hard part and has a simple plug-and-chug equation you can just use.  -- Jayron 32 16:10, 29 November 2018 (UTC)

Cure of hemiparesis
What is the state of research on treatment of hemiparesis by stem cell therapy or surgery.if a person has congenital left hemiparesis since say over 33 years and if he can walk,run and even move things and leading a normal life like completing education and doing job is it possible is it possible that with current trends of research he will get complete cure by medication/surgery/stem cell therapy/neurogenesis in his lifetime.Is research progressing in this direction that he will get a complete cure in his or lifetime with state of research in 2018.I have asked inadvertently in other section of this forum,extremely sorry because Google Scholar is incomprehensible to me so I take this opportunity to know from any of you who is knowledgeable in this field may please be kind enough to shed some light on this neglected topic.Wrogh456 (talk) 16:39, 28 November 2018 (UTC)
 * Hemiparesis is a symptom of various conditions rather than a disease unto itself, and depending on the nature of the disease which caused it may affect the treatments of it. here you can see some various sources depending on the condition, some for stroke, some for cerebral palsy.  That would be a good start for your research.  -- Jayron 32 16:45, 28 November 2018 (UTC)