Talk:Enthalpy change of solution

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Positive vs. Negative[edit]

Am I correct in thinking that a compound with a positive heat of solution will produce a cooling effect when it is dissolved in water, and vice-versa? This article seems to support that (eg. ammonium nitrate has a substantial cooling effect; it has a positive enthalpy of solution), but if this is true, then several articles (erythritol, isomalt, and probably others) and a patent (http://www.freepatentsonline.com/20050196517.html) contain glaring errors. --Pyrochem 03:09, 11 September 2007 (UTC)

You are correct. The articles on erythritol and isomalt are also correct. I haven't had time to read through the patent though. Iggwilv (talk) 03:25, 15 April 2010 (UTC)

Sodium Chloride[edit]

Hi, sodium chloride dissolved in water, has +3.89 kJ not kcal per mol, I'll change tat (data source, google, wiki german, and so on) —Preceding unsigned comment added by 77.239.33.181 (talk) 21:47, 14 January 2009 (UTC)

Sodium Hydroxide[edit]

what is value for sodium hydroxide? —Preceding unsigned comment added by 153.47.0.76 (talk) 10:22, 10 March 2009 (UTC)

I've added the value for NaOH. It's -44.51 kJ/mol in water at 25°C. --Iggwilv (talk) 17:06, 15 April 2010 (UTC)

SI units[edit]

Since this is a scientific page and scientists havnt used calories for year the given values should really be in kJ/Mol, I wont take the desision upon myself but I deffinetly support the change —Preceding unsigned comment added by 203.221.197.173 (talk) 08:28, 25 March 2009 (UTC)

The SI unit is kJ/mol. Small letter is used for m.129.94.222.43 (talk) 05:37, 26 March 2010 (UTC)

I'm going ahead and making these changes since nobody has objected. User:Iggwilv (talk) 02:58, 15 April 2010 (UTC)

Chemistry/Physics[edit]

Since this is a topic in physical chemistry, I propose that this article be placed in the Chemistry WikiProject instead of the Physics one. Iggwilv (talk) 17:28, 15 April 2010 (UTC)

Values at interim solution points[edit]

The table gives values for the full range of dilution from infinitely concentrated to infinitely diluted, which is fair enough. A description of how the delta-H changes over the range would be useful here. For example: what is the heat given off when 10N HCl is diluted to 1N HCl ? (talk) 05:41, 13 Feb 2011 (UTC)

Negative Enthalpy Change error[edit]

"Solutions with negative enthalpy changes of solution form stronger bonds and have lower vapor pressure."

Is in the article.

If a solution had a negative enthalpy change then it is exothermic. Thus it broke bonds of a higher value and formed bonds of a lower value, giving the difference off as heat. Ergo the bonds it forms will be weaker, correct? —Preceding unsigned comment added by 132.234.214.53 (talk) 11:39, 9 May 2011 (UTC)

No, because the bond breaking step is endothermic, and the bond making is exothermic, so the bond making step must have a bigger energy difference to give an overall negative enthalpy of solution. The bonds made are therefore 'stronger' Skihatboatbike (talk) 19:08, 11 March 2012 (UTC)

Comment about bond strength and vapour pressure[edit]

Hi folks, I removed this as it seemed to be without context or point of reference - the stronger bonds part of it was without reference, and the vapour pressure seemed more relevant to talk of gases which was not the specific topic in this section - all the values given in the table are for solids.Skihatboatbike (talk) 19:49, 11 March 2012 (UTC)