The first law rendered obsolete the caloric theory of heat. The caloric theory of
heat is a one-place relation theory, in which heat (or caloric) is conserved in
calorimetric processes. With the conceptual differentiation of caloric, we have the
foundation of a two-place relation “mechanical theory of heat” dealing with heat
and work, and their interconversion: the transformations of heat into mechanical
work and the opposite transformations of mechanical work into heat. In these
transformations, it is energy, rather than heat as in calorimetric processes, which is
conserved.
Production of heat, and additional comments on the transformation of heat
and work and the transformation of energy
In establishing the MEH, Joule demonstrated equivalence (i.e., equality) between
expended mechanical energy and produced heat when mechanical energy is converted into heat. In addition, Joule asserted that equality holds also during the
interconversion of heat into mechanical energy, even though he did not demonstrate
such equality during heat ! work conversion. His bold assertion of equivalence of
heat and work turned out to be true. The principle of equivalence of heat and work,
#4, Table 3.1, may be stated, as by Clausius, as,
In all cases where work is produced by heat, a quantity of heat proportional to the work
done is expended; and inversely, by the expenditure of a like quantity of work, the same
amount of heat may be produced.
This understanding and the corresponding principle of the conservation of
energy, #5, Table 3.1, represented one of the greatest achievements in the history of
science.
It is important to note, however, that whereas, for the production of heat, the
MEH teaches us it is always possible to have the complete conversion of
mechanical energy into useful heat (if all ancillary heat losses are eliminated), the
MEH, in asserting that the production of work requires the consumption (expenditure) of heat, provides no guidance as to how much of this heat is “consumed” in
the production of work. The question of the fraction of heat that may be consumed
for the production of work is to be addressed in Chaps. 4, 5, 7, and 8. In fact, the
notion that heat is expended or consumed will be called into question as to what is
really expended (see Sect. 3.11 and Chap. 8).
It should be noted furthermore that the complete statement of the principle of the
conservation of energy, as stated in #5, amounts to the idea of energy conservation
and the idea of energy availability which, strictly speaking, is beyond this chapter
and belongs to the treatment in Sect. 4.7, Chapter 4. That is, statement #5, which is
a powerful statement in its full meaning, is the most consequential statement in
thermodynamics that, in fact, captures partially the second law. For that reason, it is
the most misunderstood statement and, at the same time, the correct understanding
of which will offer true comprehension of heat and energy.
3.3 Heat Exchange and the First Law of Thermodynamics
45
heat is a one-place relation theory, in which heat (or caloric) is conserved in
calorimetric processes. With the conceptual differentiation of caloric, we have the
foundation of a two-place relation “mechanical theory of heat” dealing with heat
and work, and their interconversion: the transformations of heat into mechanical
work and the opposite transformations of mechanical work into heat. In these
transformations, it is energy, rather than heat as in calorimetric processes, which is
conserved.
Production of heat, and additional comments on the transformation of heat
and work and the transformation of energy
In establishing the MEH, Joule demonstrated equivalence (i.e., equality) between
expended mechanical energy and produced heat when mechanical energy is converted into heat. In addition, Joule asserted that equality holds also during the
interconversion of heat into mechanical energy, even though he did not demonstrate
such equality during heat ! work conversion. His bold assertion of equivalence of
heat and work turned out to be true. The principle of equivalence of heat and work,
#4, Table 3.1, may be stated, as by Clausius, as,
In all cases where work is produced by heat, a quantity of heat proportional to the work
done is expended; and inversely, by the expenditure of a like quantity of work, the same
amount of heat may be produced.
This understanding and the corresponding principle of the conservation of
energy, #5, Table 3.1, represented one of the greatest achievements in the history of
science.
It is important to note, however, that whereas, for the production of heat, the
MEH teaches us it is always possible to have the complete conversion of
mechanical energy into useful heat (if all ancillary heat losses are eliminated), the
MEH, in asserting that the production of work requires the consumption (expenditure) of heat, provides no guidance as to how much of this heat is “consumed” in
the production of work. The question of the fraction of heat that may be consumed
for the production of work is to be addressed in Chaps. 4, 5, 7, and 8. In fact, the
notion that heat is expended or consumed will be called into question as to what is
really expended (see Sect. 3.11 and Chap. 8).
It should be noted furthermore that the complete statement of the principle of the
conservation of energy, as stated in #5, amounts to the idea of energy conservation
and the idea of energy availability which, strictly speaking, is beyond this chapter
and belongs to the treatment in Sect. 4.7, Chapter 4. That is, statement #5, which is
a powerful statement in its full meaning, is the most consequential statement in
thermodynamics that, in fact, captures partially the second law. For that reason, it is
the most misunderstood statement and, at the same time, the correct understanding
of which will offer true comprehension of heat and energy.
3.3 Heat Exchange and the First Law of Thermodynamics
45