chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

and

thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed b ...

, the enthalpy of neutralization () is the change in

enthalpy Enthalpy () is the sum of a thermodynamic system's internal energy and the product of its pressure and volume. It is a state function in thermodynamics used in many measurements in chemical, biological, and physical systems at a constant extern ...

that occurs when one

equivalent Equivalence or Equivalent may refer to: Arts and entertainment *Album-equivalent unit, a measurement unit in the music industry *Equivalence class (music) *'' Equivalent VIII'', or ''The Bricks'', a minimalist sculpture by Carl Andre *'' Equiva ...

of an

acid An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...

and a base undergo a neutralization reaction to form

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

and a

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

. It is a special case of the

enthalpy of reaction The standard enthalpy of reaction (denoted \Delta H_^\ominus) for a chemical reaction is the difference between total product and total reactant molar enthalpies, calculated for substances in their standard states. The value can be approximately i ...

. 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 and 1 bar of pressure and one mole of water is formed, the heat released by the reaction is called the ''standard enthalpy of neutralization'' (). The heat () released during a reaction is :

Q = mc_p \Delta T

where is the mass of the solution, is the

specific heat capacity In thermodynamics, the specific heat capacity (symbol ) of a substance is the amount of heat that must be added to one unit of mass of the substance in order to cause an increase of one unit in temperature. It is also referred to as massic heat ...

of the solution, and is the

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

change observed during the reaction. From this, the standard enthalpy change () is obtained by division with the amount of substance (in moles) involved. :

\Delta H = - \frac

When a

strong acid Acid strength is the tendency of an acid, symbolised by the chemical formula , to dissociate into a hydron (chemistry), proton, , and an anion, . The Dissociation (chemistry), dissociation or ionization of a strong acid in solution is effectivel ...

, HA, reacts with a

strong base In chemistry, there are three definitions in common use of the word "base": '' Arrhenius bases'', '' Brønsted bases'', and '' Lewis bases''. All definitions agree that bases are substances that react with acids, as originally proposed by G. ...

, BOH, the reaction that occurs is :H+ + OH^- -> H2O as the acid and the base are fully dissociated and neither the cation nor the anion are involved in the neutralization reaction. The enthalpy change for this reaction is −57.62 kJ/mol at 25 °C. For weak acids or bases, the heat of neutralization is pH-dependent. In the absence of any added mineral acid or

alkali In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The a ...

, some heat is required for complete dissociation. The total heat evolved during neutralization will be smaller. :e.g.

\ce;\ \Delta H

= −12 kJ/mol at 25 °C The heat of ionization for this reaction is equal to (−12 + 57.3) = 45.3 kJ/mol at 25 °C.

References

{{DEFAULTSORT:Enthalpy Of Neutralization Enthalpy Thermochemistry Acid–base chemistry