Editing Acid–base reaction (section)

==Rationalizing the strength of Lewis acid–base interactions==

===HSAB theory===
{{Main|HSAB theory}}

In 1963, [[Ralph Pearson]] proposed a qualitative concept known as the [[HSAB theory|Hard and Soft Acids and Bases principle]].<ref name=pearson>{{cite journal |title=Hard and Soft Acids and Bases.|last=Pearson|first=Ralph G.|journal=[[Journal of the American Chemical Society]] |year=1963 |volume= 85 |issue=22|pages=3533–3539|doi=10.1021/ja00905a001|bibcode=1963JAChS..85.3533P }}</ref> later made quantitative with help of [[Robert Parr]] in 1984.<ref name="abshardess">{{cite journal |last1=Parr |first1=Robert G. |last2=Pearson |first2=Ralph G. |year=1983 |title=Absolute hardness: companion parameter to absolute electronegativity |journal=[[Journal of the American Chemical Society]] |volume=105 |issue=26 |pages=7512–7516 |doi=10.1021/ja00364a005|bibcode=1983JAChS.105.7512P }}</ref><ref>{{cite journal |last=Pearson |first=Ralph G. |year=2005 |title=Chemical hardness and density functional theory |url=http://www.ias.ac.in/chemsci/Pdf-sep2005/369.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.ias.ac.in/chemsci/Pdf-sep2005/369.pdf |archive-date=2022-10-09 |url-status=live |journal=[[Journal of Chemical Sciences]] |volume=117 |issue=5 |pages=369–377 |doi=10.1007/BF02708340|citeseerx=10.1.1.693.7436|s2cid=96042488 }}</ref> 'Hard' applies to species that are small, have high charge states, and are weakly polarizable. 'Soft' applies to species that are large, have low charge states and are strongly polarizable. Acids and bases interact, and the most stable interactions are hard–hard and soft–soft. This theory has found use in organic and inorganic chemistry.

===ECW model===
{{Main|ECW model}}

The [[ECW model]] created by [[Russell S. Drago]] is a quantitative model that describes and predicts the strength of Lewis acid base interactions, {{math|−Δ''H''}}. The model assigned {{mvar|E}} and {{mvar|C}} parameters to many Lewis acids and bases. Each acid is characterized by an {{math|''E''<sub>A</sub>}} and a {{math|''C''<sub>A</sub>}}. Each base is likewise characterized by its own {{math|''E''<sub>B</sub>}} and {{math|''C''<sub>B</sub>}}. The {{mvar|E}} and {{mvar|C}} parameters refer, respectively, to the electrostatic and covalent contributions to the strength of the bonds that the acid and base will form. The equation is
<math display=block>-\Delta H = E_{\rm A}E_{\rm B} + C_{\rm A}C_{\rm B} + W</math>

The {{mvar|W}} term represents a constant energy contribution for acid–base reaction such as the cleavage of a dimeric acid or base. The equation predicts reversal of acids and base strengths. The graphical presentations of the equation show that there is no single order of Lewis base strengths or Lewis acid strengths.<ref>{{cite journal|author1=Vogel G. C. |author2=Drago, R. S.|year=1996|journal=Journal of Chemical Education|volume=73|issue=8|pages=701–707|title=The ECW Model|bibcode=1996JChEd..73..701V|doi=10.1021/ed073p701}}</ref>