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2 Macroscopic Thermodynamics
based upon a fundamental set of (three) laws, referred to as the three Laws of
Thermodynamics, plus an additional postulate, sometimes referred to as the zeroth
law of thermodynamics. Before proceeding with a discussion of thermodynamics,
however, we shall require definitions of a number of traditional terms that are
typically employed in this discipline. More extensive discussions of the fundamental
aspects of thermodynamics can be found in Ref. [5–7].
2.1 Basic Thermodynamic Definitions
The term thermodynamic system 1 refers to a (macroscopic) portion of the physical
world that can be fully described in terms of a set of its physical attributes referred to
as thermodynamic variables; the rest of the physical world, with which a system of
interest is in contact (and with which it may in general exchange energy and mass)
is referred to as the surroundings. A gross characterization of such systems may be
made on the basis of how they interact with their surroundings. For example, two
systems are said to be in thermal contact if the only interactions between them
involve no exchange of matter and involve energy transfers that do not require
work to be done by one system on the other. In general, systems fall into three
categories: a system that is incapable of exchanging either energy or mass with
its surroundings is said to be an isolated system, a system that is only in thermal
contact with its surroundings is said to be a closed system and, finally, a system that
may exchange both energy and mass with its surroundings is said to be an open
system. We shall have occasion to encounter all three of these categories, although
not always necessarily in the context of macroscopic thermodynamics.
A more refined characterization of a particular system may be carried out in
terms of the physical properties associated with a set of macroscopic coordinates,
by which we mean coordinates that are determined via measurements representing
averages over regions of space containing many atoms and/or molecules and over
time spans that are many orders of magnitude longer than those associated with
particle motions. In addition, we shall be concerned with changes that involve
macroscopically large amounts of energy. Physical properties that have been
characterized in this manner are then termed thermodynamic properties, and are
further categorized as intensive if they are independent of the mass of the system
(examples are pressure, P , and temperature, T , which we know from experiment
are independent of the mass/size of the thermodynamic system) and as extensive if
they do depend upon the mass of the system (such as the volume, V , and number
of atoms or molecules, N). 2 This characterization is often referred to loosely as
‘size dependence’. However, it is worth noting that the determination of extensivity
requires all intensive properties to be held fixed.
1 For simplicity, we shall henceforth often refer to a ‘thermodynamic system’ simply as a ‘system’.
2 See also the discussion at the end of subsection (vi) of Sect. B.1.2.
2 Macroscopic Thermodynamics
based upon a fundamental set of (three) laws, referred to as the three Laws of
Thermodynamics, plus an additional postulate, sometimes referred to as the zeroth
law of thermodynamics. Before proceeding with a discussion of thermodynamics,
however, we shall require definitions of a number of traditional terms that are
typically employed in this discipline. More extensive discussions of the fundamental
aspects of thermodynamics can be found in Ref. [5–7].
2.1 Basic Thermodynamic Definitions
The term thermodynamic system 1 refers to a (macroscopic) portion of the physical
world that can be fully described in terms of a set of its physical attributes referred to
as thermodynamic variables; the rest of the physical world, with which a system of
interest is in contact (and with which it may in general exchange energy and mass)
is referred to as the surroundings. A gross characterization of such systems may be
made on the basis of how they interact with their surroundings. For example, two
systems are said to be in thermal contact if the only interactions between them
involve no exchange of matter and involve energy transfers that do not require
work to be done by one system on the other. In general, systems fall into three
categories: a system that is incapable of exchanging either energy or mass with
its surroundings is said to be an isolated system, a system that is only in thermal
contact with its surroundings is said to be a closed system and, finally, a system that
may exchange both energy and mass with its surroundings is said to be an open
system. We shall have occasion to encounter all three of these categories, although
not always necessarily in the context of macroscopic thermodynamics.
A more refined characterization of a particular system may be carried out in
terms of the physical properties associated with a set of macroscopic coordinates,
by which we mean coordinates that are determined via measurements representing
averages over regions of space containing many atoms and/or molecules and over
time spans that are many orders of magnitude longer than those associated with
particle motions. In addition, we shall be concerned with changes that involve
macroscopically large amounts of energy. Physical properties that have been
characterized in this manner are then termed thermodynamic properties, and are
further categorized as intensive if they are independent of the mass of the system
(examples are pressure, P , and temperature, T , which we know from experiment
are independent of the mass/size of the thermodynamic system) and as extensive if
they do depend upon the mass of the system (such as the volume, V , and number
of atoms or molecules, N). 2 This characterization is often referred to loosely as
‘size dependence’. However, it is worth noting that the determination of extensivity
requires all intensive properties to be held fixed.
1 For simplicity, we shall henceforth often refer to a ‘thermodynamic system’ simply as a ‘system’.
2 See also the discussion at the end of subsection (vi) of Sect. B.1.2.