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Thermodynamics in GeochemistryThe Equilibrium Model$
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Greg M. Anderson and David A. Crerar

Print publication date: 1993

Print ISBN-13: 9780195064643

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195064643.001.0001

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The First Law of Thermodynamics

The First Law of Thermodynamics

Chapter:
(p.60) 4 The First Law of Thermodynamics
Source:
Thermodynamics in Geochemistry
Author(s):

Greg M. Anderson

David A. Crerar

Publisher:
Oxford University Press
DOI:10.1093/oso/9780195064643.003.0008

We have by now amassed sufficient definitions and reviewed enough mathematics to begin discussion of energy levels and transfers. This is a very difficult subject, as evidenced by the fact that more than 50 years of scientific effort were required before the relationships between heat, work, and energy were well understood. A knowledge of the history of development of this understanding by Carnot, Mayer, Rumford, Clausius, Joule, Thompson, and others is very helpful in appreciating the significance of the First Law of thermodynamics. Part of the difficulty lies in the fact that the concepts of temperature, heat and work are so intuitively familiar to us that we tend to use them without much thought. We have already discussed systems in terms of heat transfer just as if we knew exactly what heat is. We present here a summary of the present understanding of the relation between heat, work, and energy levels of systems, leading to a definition of the first law of thermodynamics. We are all familiar with the sensation of warmth, that is, that some objects are hotter or colder than others. A large number of instruments called thermometers can be (and have been) devised which will indicate degrees of hotness or coldness of their environments. They have physical properties which vary perceptibly as they become hotter or colder (examples are the volume of a body of fluid at a fixed pressure, the length of a column of mercury in a glass tube, or the voltage produced by a metallic couple); these changes can be assigned arbitrary units of "hotness." The zeroth law says that two bodies that are in thermal equilibrium with a third body are in equilibrium with each other. By thermal equilibrium we mean that two bodies are in contact separated by a wall or walls that prevent exchange of mechanical energy or mass, but which still allow the two bodies to interact energetically. Such walls are called diathermal, that is, they allow heat to flow between the bodies. When no further change in the bodies is observed, they are at equilibrium; if one of these is a thermometer, its properties (volume, length, voltage) have been calibrated according to some arbitrary scale, and a reading on this "hotness" or temperature scale may be made.

Keywords:   first law, internal energy, potential energy, rest energy, thermometer, zeroth law

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