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Enthalpy
In thermodynamics, enthalpy, symbolized by H, summarized as ‘heat content’, is defined as the sum of the internal energy of a thermodynamic system plus the energy associated with work done by the system on the atmosphere, i.e. the product of the pressure times the volume. Enthalpy reflects the number and kinds of chemical bonds in the reactants and products. [1] In equation form, enthalpy is defined as follows:
The quantity H, equal to the internal energy plus the pressure volume energy, was first recognized by Gibbs as playing an important role for processes occurring at constant pressure, and was called by him ‘heat content’. Some years later, in 1909, the Dutch physicist Kamerlingh-Onnes gave H the name enthalpy, from the Greek εν (en) ‘in’ and θαλπος (thalpos) ‘to heat’, which combined define the word enthalpos, to warm within.
In biochemical thermodynamics, enthalpy is considered as a ‘thermodynamic state function usually measured as heat transferred to or from a system at constant pressure.’ [2] With the constraints of constant pressure and amount of substance, the differential change in enthalphy dH, of a system evolving in such conditions, equals the amount of heat dQP exchanged with the surroundings.’ [3]
References
1. Lehninger, A.L., Nelson, D.L., & Cox, M.M. (1993). Principles of Biochemistry, 2nd ed. New York: Worth Publishers.
2. Haynie, D.T. (2001). Biological Thermodynamics. Cambridge: Cambridge University Press.
3. Perrot, P. (1998). A to Z of Thermodynamics. Oxford: Oxford University Press.
H = U + PV
The quantity H, equal to the internal energy plus the pressure volume energy, was first recognized by Gibbs as playing an important role for processes occurring at constant pressure, and was called by him ‘heat content’. Some years later, in 1909, the Dutch physicist Kamerlingh-Onnes gave H the name enthalpy, from the Greek εν (en) ‘in’ and θαλπος (thalpos) ‘to heat’, which combined define the word enthalpos, to warm within.
In biochemical thermodynamics, enthalpy is considered as a ‘thermodynamic state function usually measured as heat transferred to or from a system at constant pressure.’ [2] With the constraints of constant pressure and amount of substance, the differential change in enthalphy dH, of a system evolving in such conditions, equals the amount of heat dQP exchanged with the surroundings.’ [3]
References
1. Lehninger, A.L., Nelson, D.L., & Cox, M.M. (1993). Principles of Biochemistry, 2nd ed. New York: Worth Publishers.
2. Haynie, D.T. (2001). Biological Thermodynamics. Cambridge: Cambridge University Press.
3. Perrot, P. (1998). A to Z of Thermodynamics. Oxford: Oxford University Press.
Latest page update: made by Sadi-Carnot
, Jun 22 2008, 1:18 AM EDT
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