Editing Enthalpy of neutralization

{{Short description|Change in enthalpy during an acid-base reaction}}

In [[chemistry]] and [[thermodynamics]], the '''enthalpy of neutralization''' ({{math|Δ{{sub|n}}''H''}}) is the change in [[enthalpy]] that occurs when one [[Equivalent (chemistry)|equivalent]] of an [[acid]] and a [[Base (chemistry)|base]] undergo a [[neutralization reaction]] to form [[water]] and a [[Salt (chemistry)|salt]]. It is a special case of the [[enthalpy of reaction]]. It is defined as the energy released with the formation of 1 mole of water.
When a reaction is carried out under [[standard conditions]] at the temperature of {{convert|298|K|C}} and 1 [[bar (unit)|bar]] of pressure and one mole of water is formed, the heat released by the reaction is called the ''standard enthalpy of neutralization'' ({{math|Δ{{sub|n}}''H''{{sup|⊖}}}}).

The heat ({{mvar|Q}}) released during a reaction is
:<math> Q = mc_p \Delta T </math>

where {{mvar|m}} is the mass of the solution, {{mvar|c{{sub|p}}}} is the [[specific heat capacity]] of the solution, and {{math|∆''T''}} is the [[temperature]] change observed during the reaction. From this, the standard enthalpy change ({{math|∆''H''}}) is obtained by division with the amount of substance (in [[mole (chemistry)|moles]]) involved.

:<math> \Delta H = - \frac{Q}{n} </math>
When a [[strong acid]], HA, reacts with a [[strong base]], BOH, the reaction that occurs is
:<chem>H+ + OH^- -> H2O</chem>    
as the acid and the base are fully dissociated and neither the cation {{chem2|B+}} nor the anion {{chem2|A-}} are involved in the neutralization reaction.<ref name="chemguide">{{cite web |url=https://www.chemguide.co.uk/physical/energetics/neutralisation.html |title=Enthalpy Change of Neutralization |last=Clark |first=Jim |date=July 2013 |website=chemguide.co.uk |access-date=4 September 2019}}</ref> The enthalpy change for this reaction  is −57.62 kJ/mol at 25&nbsp;°C.

For [[weak acids]] or [[Weak base|bases]], the heat of neutralization is pH-dependent.<ref name="chemguide" /> In the absence of any added mineral acid or [[alkali]], some heat is required for complete dissociation. The total heat evolved during neutralization will be smaller.

:e.g. <math chem>\ce{HCN + NaOH -> NaCN + H2O};\ \Delta H</math> = −12&nbsp;kJ/mol at 25&nbsp;°C

The [[Ionization energy|heat of ionization]] for this reaction is equal to (−12 + 57.3) = 45.3 kJ/mol at 25&nbsp;°C.<ref name="Community College of Rhode Island">{{cite web |title=Enthalpy of Neutralization |url=http://faculty.ccri.edu/aahughes/GenChemII/Lab%20Experiments/Enthalpy_of_Neutralization.pdf |publisher=Community College of Rhode Island |accessdate=24 February 2014 |archive-url=https://web.archive.org/web/20161213060740/http://faculty.ccri.edu/aahughes/GenChemII/Lab%20Experiments/Enthalpy_of_Neutralization.pdf |archive-date=13 December 2016 |url-status=dead }}</ref>

==References==
{{Reflist}}

{{DEFAULTSORT:Enthalpy Of Neutralization}}
[[Category:Enthalpy]]
[[Category:Thermochemistry]]
[[Category:Acid–base chemistry]]