# reaction enthalpyZoomA-Z

## Subject - Physical Chemistry, Thermodynamics

The differential reaction enthalpy $ΔrH$ is a partial differential quotient of the total differential of the state function $H=H(p,T,ξ)$. To demonstrate, this differential quotient is represented as a sum of the partial molar enthalpies of educts and products.

$ΔrH=(∂H∂ξ)p,T=∑iνiHpart,iΔr=∂∂ξ=differential operatorξ=turnover variablep=pressureT=absolute temperatureνi=stoichiometric numberHpart,i=partial molar enthalpies of substance i$

The sum of partial molar enthalpies (partial molar size) can be written as a difference because the stoichiometric numbers of products are counted as positive while those of the educts enter the equation as negatives.

$∑iνiHpart,i=∑i(|νi|Hpart,i)Pr⁡o−∑i(|νi|Hpart,i)Edu$

In case of an ideal reaction mixture, partial molar enthalpies can be substituted with molar enthalpies.

The integral reaction enthalpy $ΔH$ is obtained by integration of the differential reaction enthalpies.

$ΔH=∫ξ1ξ2ΔrHdξ=H(ξ2)−H(ξ1)Δ=symbol for difference$

Frequently, the integral reaction enthalpy is described as the difference of molar enthalpies of the starting materials (products) and end products (educts) of a chemical reaction.

$ΔH=∑i(niHm,i)Pr⁡o−∑i(niHm,i)Edu$

Molar instead of partial values can be used when assuming ideal conditions of the reaction mixture.

The integral reaction enthalpy is determined by measuring the heat of reaction of a reaction. reactions show a positive enthalpy while reactions with negative enthalpy are called reactions.

If the pressure during the reaction remains constant, the integral reaction enthalpy equals the heat of reaction $Qp$ being given or taken up by the reaction.

$ΔH=±Qp$