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CHAPTER 1
Gibbs Energy and Helmholtz Energy: Introduction, Concepts and Selected Applications
EMMERICH WILHELM*a
a Institute of Materials Chemistry and Research, University of Vienna, Währinger Strasse 42, A-1090 Wien (Vienna), Austria,
*E-mail:
[email protected] Thermodynamics is a science of bulk matter (solid, liquid, gaseous) presuming no detailed information on the microscopic structure of matter: it provides mathematical relations between macroscopic observable properties that are invariable to all changes in microscopic concepts. Thermodynamic theory is applicable to all types of macroscopic matter, irrespective of its chemical composition and independent of molecule-based information â this is the strength of thermodynamics and the basis of its enormous generality. Using an axiomatic approach, this chapter presents systematically and concisely essential parts of classical thermodynamics applicable to non-electrolyte fluids, pure and mixed. All fundamental property relations in the internal energy representation as well as in the entropy representation are derived via Legendre transformation. Residual properties in (T,P,x)-space, in (T,V,x)-space and in (T,Ď,x)-space are presented and their relations to fugacities and fugacity coefficients are established. In addition, property changes on mixing, excess properties and LewisâRandall activity coefficients are discussed. Finally, several topics of current interest in molecular thermodynamics are considered, such as internal pressure, solubility parameter and equations of state.
Tyger, Tyger, burning bright,
In the forests of the night
What immortal hand or eye,
Could frame thy fearful symmetry?
William Blake
(London, 28 November 1757â12 August 1827)
The poem The Tyger (six stanzas in length, each stanza four lines long) was published in 1794 as part of Blake's illuminated book Songs of Experience (a sequel to Songs of Innocence, published in 1789). Reproduced from Songs of Experience, quotation in the public domain.
1.1 Introduction
The two fundamental disciplines representing the scientific basis of chemistry are quantum mechanics and thermodynamics. Whereas the former focuses on the properties and behaviour of the microscopic constituents of matter, that is, on atoms, molecules and electrons in the realm of chemistry, the latter is concerned with macroscopic or bulk properties and behaviour and does not consider the microscopic state of matter at all. By bridging the gap between them, statistical mechanics is used to reconcile these two extremes. Based entirely on experiments on macroscopic systems, that is, on fundamental laws extracted therefrom, thermodynamics is a formalised phenomenological theory of enormous generality in the following sense:
- The remarkable feature of thermodynamics is its independence from any microscopic assumptions: it provides us with mathematical relations between macroscopic properties that are invariable to all changes in microscopic molecular models. Thermodynamic theory is applicable to all types of macroscopic matter, irrespective of its chemical composition and independent of molecule-based information, i.e. systems are treated as âblack boxesâ and the concepts used ignore the existence of molecules and indeed do not need it: thermodynamic relations would correctly describe macroscopic reality if matter were continuous. Although thermodynamics alone does not provide any molecular information, this is not a disadvantage. Consider, for instance, (biological) systems that are too complicated to be adequately des...
