The physical and chemical processes heat is transferred from one body to another.It is possible, usually at constant pressure and temperature.In the role of a constant pressure is usually an atmospheric pressure.The enthalpy as the internal energy is a function of sostoyaniya.Vnutrennyaya energy is the sum of kinetic and potential energies of the entire system.It is the basis for equation enthalpy.Enthalpy is the sum of the internal energy and pressure multiplied by the volume of the system and is equal to: H = U + pV, where p - the system pressure, V - volume sistemy.Vysheukazannaya formula is used to calculate the enthalpy when all three
values ​​are: pressure, volume and internal energy.However, it is not always the enthalpy is calculated in such a way.Besides it, there are several ways to calculate enthalpy.
Knowing the free energy and entropy and enthalpy can be calculated .The free energy or Gibbs energy is a part of the enthalpy of the system spent on the transformation of the work, and is equal to the difference between the enthalpy and the temperature times the entropy: ΔG = ΔH-TΔS (ΔH, ΔG, ΔS - incremental value) Entropy in the formula isa measure of disorder in a system of particles.It increases with the temperature T and pressure.When ΔG & lt; 0, the process is spontaneous when ΔG & gt; 0 - do not go.
In addition, the enthalpy as calculated from the equation of chemical reaction.If an equation of the chemical reaction of the form A + B = C, then enthalpy can be determined by the formula: dH = dU + ΔnRT, where Δn = nk-NH (nk and ni - the number of moles of reaction products and starting materials) are isobaric process entropyequal to the change in the heat: dq = dH.Pri constant pressure, enthalpy is: H = ∫SpdTV if the enthalpy and entropy factors balance each other, the change of enthalpy is the product of the temperature on the increase of entropy: ΔH = TΔS