Enthalpy and Internal Energy

Liquids, Solutions and Vapours

Emmerich Wilhelm, Trevor Letcher, Emmerich Wilhelm, Trevor Letcher

• Verlag: Royal Society of Chemistry
• Jahr: 2017
• ISBN:
  9781788011969
• Auflage: 1
• Thema: Physical Sciences
• Thema: Physical & Theoretical Chemistry

Containing the very latest information on all aspects of enthalpy and internal energy as related to fluids, this book brings all the information into one authoritative survey in this well-defined field of chemical thermodynamics. Written by acknowledged experts in their respective fields, each of the 26 chapters covers theory, experimental methods and techniques and results for all types of liquids and vapours. These properties are important in all branches of pure and applied thermodynamics and this vital source is an important contribution to the subject hopefully also providing key pointers for cross-fertilization between sub-areas.

CHAPTER 1

Internal Energy and Enthalpy: Introduction, Concepts and Selected Applications

EMMERICH WILHELM

Institute of Materials Chemistry & Research/Institute of Physical Chemistry, University of Wien, Währinger Strasse 42, A-1090, Wien (Vienna)Austria
Email: [email protected]

1.1 Introduction

Life is girt all round with a zodiac of sciences, the contributions of men who have perished to add their point of light to our sky.
Ralph Waldo Emerson, Representative Men. Seven Lectures: I. Uses of Great Men, The Riverside Press, Cambridge, Mass., USA (1883).

This monograph is concerned with internal energy and enthalpy and related properties of fluids, pure and mixed, and their role in the physico-chemical description of systems ranging from pure rare gases to proteins in solution. In this introductory Chapter 1, I shall only consider nonreacting fluid equilibrium systems of uniform temperature T and pressure P (i.e., systems in thermal, mechanical and diffusional equilibrium) characterised by the essential absence of surface effects and extraneous influences, such as electric fields. However, the influence of the earth's gravitational field is omnipresent: though usually ignored, it becomes important near a critical point. Under ordinary conditions, the molar volumes V (or specific volumes V/m_m, where m_m denotes the molar mass) of homogeneous fluids in equilibrium states are functions of T, P and composition only. Such systems are known as PVT systems or simple systems. However, the generality of thermodynamics makes it applicable to considerably broader types of systems by adding appropriate work terms, i.e., products of conjugate intensive and extensive variables, such as surface tension and area of surface layer. Finally, there is a caveat concerning idealised concepts for systems and processes, such as isolated systems, isothermal and reversible processes, to name but a few. Fortunately, they can be well approximated experimentally, and while classical thermodynamics only treats the corresponding limiting cases, the ensuing restrictions are not severe: values of thermodynamic quantities obtained with different experimental techniques are expected to agree within experimental error. Classical thermodynamics deals only with measurable equilibrium properties of macroscopic systems. It is a formalised phenomenological theory of enormous generality in the following sense:

• 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 “black boxes” and the concepts used ignore microscopic structure, and indeed do not need it.
• Classical thermodynamics does not allow ab initio prediction of numerical values for thermodynamic properties. It ...