Volume 13 (2017)
PROGRESS IN PHYSICS
Issue 3 (July)
A New Perspective for Kinetic Theory and Heat Capacity
Kent W. Mayhew
68 Pineglen Cres., Ottawa, Ontario, K2G 0G8, Canada. E-mail: Kent.Mayhew@gmail.com
The currently accepted kinetic theory considers that a gas’ kinetic energy is purely translational and then applies equipartition/degrees of freedom. In order for accepted theory
to match known empirical finding, numerous exceptions have been proposed. By redefining the gas’ kinetic energy as translational plus rotational, an alternative explanation for kinetic theory is obtained, resulting in a theory that is a better fit with empirical
findings. Moreover, exceptions are no longer required to explain known heat capacities.
Other plausible implications are discussed.
1 Introduction
Various explanations for equipartition’s failure in describing
heat
capacities have been proposed. Boltzmann suggested
The conceptualization of a gaseous system’s kinematics origthat
the
gases
might not be in thermal equilibrium [8]. Planck
inated in the writings of the 19th century greats. In 1875,
[9]
followed
by
Einstein and Stern [10] argued the possibility
Maxwell [1] expressed surprise at the ratio of energies (transof
zero-point
harmonic
oscillator. More recently Dahl [11]
lational, rotational and/or vibrational) all being equal. Boltzhas
shown
that
a
zero
point
oscillator to be illusionary. Lord
mann’s work on statistical ensembles reinforced the current
Kelvin
[12–13]
realized
that
equipartition maybe wrongly deacceptance of law of equipartition with a gas’s energy being
rived.
The
debate
was
somewhat
ended by Einstein claiming
equally distributed among all of its degrees of freedom [2–3].
that
equipartition’s
failure
demonstrated
the need for quantum
The net result being that the accepted mean energy for each
theory
[14–15].
Heat
capacities
of
gases
have been studied
independent quadratic term being kT/2.
throughout
the
20th
century
[16–19]
with
significantly more
The accepted empirically verified value for the energy of
complex
models
being
developed
[20–21].
a /textitN molecule monatomic gas is kT/2 with its isometIt becomes a goal of this paper to clearly show that an
ric molar heat capacity (Cv ) being (3R/2). An implication
alternative
kinetic theory/model exists. A simple theory that
is that a monatomic gas only possesses translational energy
correlates
better
with empirical findings without relying on
[4–5]. The reasoning for this exception is that the radius of a
exceptions
while
correlating with quantum theory.
monatomic gas is so small that its rotational energy remains
negligible, hence its energy contribution is simply ignored.
2 Kinetic theory and heat capacity simplified
Mathematically speaking equipartition based kinetic theory states that a molecule with n′′ atoms has 3n′′ degrees of Consider wall molecules 1 through 8, in Fig. 1. The total
mean energy along the x-axis of a vibrating wall molecule is
freedom (f ) [5–6] i.e.:
f = 3n′′ .
(1)
E x = kT.
(3)
This leads to the isometric molar heat capacity (Cv ) for large Half of a wall molecule’s mean energy would be kinetic enpolyatomic molecules:
ergy, and half would be potential energy. Thus, the mean
3 ′′
kinetic energy along the x-axis, remains
Cv = n R.
(2)
2
kT
.
(4)
Ex =
Interestingly, the theoretical expected heat capacity for N di2
atomic molecules is 7NkT/2. This is the summation of the
following three energies a) three translational degrees, i.e. In equilibrium, the mean kinetic energy of a wall molecule, as
3NkT/2. b) three rotational degrees of freedom, however defined by equation (4) equals the mean kinetic energy of the
since the moment of inertia about the internuclear axis is van- gas molecule along the same x-axis. Herein, the wall in the
ishing small w.r.t. other moments, then it is excluded, i.e. y-z plane acts as a massive pump, pumping its mean kinetic
NkT . c) Vibrational energy, i.e. NkT . This implies a molar energy along the x-axis onto the much smaller gas molecules.
In equilibrium each gas molecule will have received a
heat capacity Cv =7NkT/2 = 29.3 J/(mol*K). However, empirical findings indicate that the isometric molar heat capacity component of kinetic energy along each orthogonal axis. Alfor a diatomic gas is actually 20.8 J/(mol*K), which equates though there are six possible directions, at any given instant,
to 5RT/2 [6]. This discrepancy for diatomic gases certainly a gas molecule can only have components of motion along
allows one to question the precise validity of accepted kinetic three directions, i.e. it cannot be moving along both the postheory! In 1875 Maxwell noted that since atoms have internal itive and negative x-axis at the same time. Therefore, the
parts then this discrepancy maybe worse than we believe [7]. total kinetic energy of the N molecule gas is defined by
166
Kent Mayhew. A New Perspective for Kinetic Theory and Heat Capacity
Issue 3 (July)
PROGRESS IN PHYSICS
Volume 13 (2017)
Fig. 1: Ideal monoatomic gas at pressure Pg and temperature T g
sourrounded by walls at temperature T w = T g . Gas molecules have
no vibrational energy.
Fig. 2: Ideal diatomic gas at pressure Pg and temperature T g sourrounded by walls at temperature T w = T g . Gas molecules have vibrational energy.
equation (4) i.e. 3NkT/2. Up to this point we remain in
agreement with accepted theory.
Consider that you hit a tennis ball with a suitable racquet.
If the ball impacts the racquet’s face at a 90 degree angle, then
the ball will have significant translational energy in comparison to any rotational energy. Conversely, if the ball impacts
the racquet at an acute angle, although the same force is imparted onto that ball, the ball’s rotational energy can be significant in comparison to its translational energy. The point
being, in real life both the translational and rotational energy,
are due to the same impact.
Now reconsider kinetic theory. Understandably, momentum transfer between both the wall’s and gas’ molecules result in energy exchanges between the massive wall and small
gas molecules. Moreover, the exact nature of the impact will
vary, even though the exchanged mean energy is constant.
it cannot rotate hence both energies can only result in
vibrational energy of the wall molecules along its three
orthogonal axis.
After numerous wall impacts, our model predicts that an
N molecule monatomic gas will have a total kinetic energy
(translational plus rotational) defined by
EkT (t,r) =
3
NkT.
2
(5)
Fig. 2 illustrates a system of diatomic gas molecules in a container. The wall molecules still pass the same mean kinetic
energy onto the diatomic gas molecule’s center of mass with
each collision. Therefore the diatomic gas’ kinetic energy is
defined by equation (5). The diatomic gas molecule’s vibrational energy would be related to the absorption and emission of its surrounding blackbody/thermal radiation. Therefore, the mean x-axis vibrational energy within a diatomic gas
Case 1: Imagine that a monatomic gas molecule collides
molecule remains defined by equation (3) and the total mean
head on with a wall molecule, e.g. the gas molecule
energy for a diatomic gas molecule becomes defined by
hitting wall molecule no. 3 in Fig. 1. Herein, the gas
3
5
molecule might only exchange translational energy
E tot = E kT (t,r) + E v = kT + kT = kT.
(6)
with the wall, resulting in the gas molecule’s mean ki2
2
netic energy being purely translational, and defined by Therefore the total energy for an N molecule diatomic gas
equation (4).
becomes
Case 2: Imagine that a monatomic gas molecule strikes wall
3
5
Etot = EkT (t,r) + Ev = NkT + NkT = NkT.
molecule no. 1 at an acute angle. The gas molecule
2
2
would obtain both rotational and translational energy
from the impact such that the total resultant mean en- For an N molecule triatomic gas:
ergy of the gas molecule would be the same as it was
7
3
Etot = EkT (t,r) + Ev = NkT + 2NkT = NkT,
in Case 1, i.e. defined by equation (4).
2
2
Case 3: Imagine a rotating and translating monatomic gas
molecule striking the wall. Both the rotational and translational energies will be passed onto the wall molecule. Since the wall molecule is bound to its neighbors,
(7)
(8)
n′′ signifies the polyatomic number. Therefore for N
molecules of n′′ -polyatomic gas, the vibrational energy is
Kent Mayhew. A New Perspective for Kinetic Theory and Heat Capacity
Ev = (n′′ − 1)NkT.
(9)
167
Volume 13 (2017)
PROGRESS IN PHYSICS
Issue 3 (July)
acetylene (C2 H2 , n′′ = 4, Cv = 35.7) are linear bent molecules
and good fit, while pyramidal ammonia (NH3 , n′′ = 4, Cv =
3
′′
27.34) is not. Could the gas molecule’s shape influence how
NkT + (n − 1) NkT
Etot = EkT (t,r) + Ev =
2
!
(10) it absorbs surrounding thermal radiation, hence its vibrational
1
energy?
= n′′ +
NkT.
2
Table 2 shows the accepted adiabatic index versus our
theoretical adiabatic index for most of the same substances
Dividing both sides by temperature and rewriting in terms of
shown in Table 1. Our theoretical adiabatic index compares
per mole (N=6.02 × 1023 ) then equation (10) becomes:
rather well with the accepted empirical based values, espe!
!
cially for low n′′ < 4 and high n′′ > 11, as is clearly seen
1
1
Etot
= R n′′ +
.
(11) in Fig. 4. Although not 100% perfect, this new theory/model
= nk n′′ +
T
2
2
certainly warrants due consideration by others.
For most temperature regimes, the heat capacity of gases
3 Kinetic theory and thermal equilibrium
remains fairly constant, hence equation (11) can be rewritten
Kinetic theory holds because the walls act as massive energy
in terms of the isometric molar heat capacity (Cv ), i.e.
pumps, i.e. gas molecules take on the wall’s energy with ev!
1
ery gas-wall collision. For sufficiently dilute gases, this re′′
Cv = R n +
.
(12)
mains the dominant method of energy exchange. Mayhew
2
[23–24] has asserted that inter-gas molecular collisions tend
The difference between molar isobaric heat capacity (C p ) and to obey conservation of momentum, rather than adhere to kimolar isometric heat capacity (Cv ) for gases is the ideal gas netic theory. Therefore, when inter-gas collisions dominate
constant (R) [see equation (15)]. Therefore, a gas’s isobaric over gas-wall collisions, then kinetic theory, the ideal gas law,
heat capacity C p becomes
Avogadro’s hypothesis, Maxwell’s velocities etc. all can start
!
!
to lose their precise validity.
3
1
It is accepted that there are changes to heat capacity in
+ R = R n′′ +
.
(13)
C p = R n′′ +
2
2
and around dissociation temperatures. Firstly, at such high
temperatures, the pressure tends to be high; hence the interThe adiabatic index is the ratio of heat capacities, i.e. dividing
gas collisions may dominate. This author believes that this
equation (13) by equation (12) gives the adiabatic index
actually helps explain why kinetic theory falters in polytropic
stars, wherein high-density gases collide in a condensed mat3
′′
n +2
Cp
.
γ=
(14) ter fashion hence one must use polytropic solutions. Sec=
Cv
n′′ + 12
ondly, at high temperatures a system’s thermal energy density
is no longer proportional to temperature, i.e. a blast furnace’s
Table 1 shows the accepted isometric and isobaric mo- thermal energy density is proportional to T 4 [22].
lar heat capacities for various substances for 0 > n′′ > 27.
Blackbody radiation describes the radiation within an enThese values were calculated using data (specific heats) from closure. For an open system and/or none blackbody, the theran engineering table (Rolle [22]) that is shown in Table 2. mal radiation surrounding the gas molecules may be better
Note: Engineer’s use specific heats (per mass), physicists and to considered. Herein thermal radiation means radiation that
chemists prefer heat capacity (per mole).
is readily absorbed and radiated by condensed matter and/or
In Fig. 3, both our theoretical molar isometric and isobaric polyatomic gases, resulting in both intramolecular and inter[equations (12) and (13)] heat capacities are plotted against molecular vibrations.
the number of atoms (n′′ ) in each molecule. The accepted
For a system of dilute polyatomic gas e.g. Fig. 2, therempirically determined values for heat capacities versus n′′ mal equilibrium requires that all of the following three states
(from Table 1) are also plotted. The traditional theoretical remain related to the same temperature (T):
values for molar heat capacities [eq. (2)] are also plotted.
1. The walls are in thermal equilibrium with the enclosed
The theory/model proposed herein remains a better fit to
blackbody/thermal radiation.
empirical findings for all polyatomic molecules. Importantly,
2. The gas’ translational plus rotational energy is in meit does not rely upon the exceptions that plague the traditionchanical equilibrium with the molecular vibrations of
ally accepted degrees of freedom based kinetic theory.
the walls.
Interestingly, there is a discrepancy, between our model
′′
3.
The
gas’ vibrational energies are in thermal equiliband empirical known values for 4 < n < 9. Moreover,
rium
with the enclosed blackbody/thermal radiation.
the slope of our theoretical values visually remains close to
′′
the slope of empirically determined values for n > 8. FurImagine that a system of dilute polyatomic gas is taken
thermore, hydrogen peroxide (H2 O2 , Cv = 37.8, n′′ = 4) and to remote outer space, and that the walls are magically reTherefore, the total energy for a polyatomic gas molecule is:
168
Kent Mayhew. A New Perspective for Kinetic Theory and Heat Capacity
Issue 3 (July)
PROGRESS IN PHYSICS
Volume 13 (2017)
Table 1: Accepted isometric and isobaric heat capacities versus theoretical i.e. empirical findings versus Eqn. (12), Eqn. (13), as well as
Eqn. (2). Note: Accepted heat capacities were calculated from the engineer’s specific heats in Table 2 (Rolle [22]), exception being H2 O2
which was taken from Giguere [19].
n′′
Accepted
Cv
[J/mol*K]
Eqn. (12)
Cv
[J/mol*K]
Accepted
Cp
[J/mol*K]
Eqn. (13)
Cp
[J/mol*K]
Substance
Eqn. (2)
Cv
[J/mol*K]
Helium
He
1
12.48
12.47
20.80
20.78
Neon
Ne
1
12.47
12.47
20.79
20.78
Argon
Ar
1
12.46
12.47
20.81
20.78
Xenon
Xe
1
12.47
12.47
20.58
20.78
Hydrogen
H2
2
20.52
20.78
28.83
29.09
Nitrogen
N2
2
20.82
20.78
29.14
29.09
Oxygen
O2
2
21.02
20.78
29.34
29.09
Nitric oxide
NO
2
21.55
20.78
29.86
29.09
Water vapor
H2 O
3
25.26
29.09
33.58
37.40
37.40
Carbon dioxide
CO2
3
28.83
29.09
37.14
37.40
37.40
Sulfur dioxide
SO2
3
31.46
29.09
39.78
37.40
37.40
Hydrogen peroxide
H2 O2
4
37.4
37.73
46.05
45.71
49.86
Ammonia
NH3
4
27.37
37.40
35.70
45.71
49.86
Methane
CH4
5
27.4
45.71
35.72
54.0
62.33
Ethylene
C2 H4
6
35.24
54.02
43.54
62.33
74.79
Ethane
C2 H6
8
44.35
70.64
52.65
78.95
99.72
Propylene
C3 H6
9
53.82
78.95
63.92
87.26
112.19
Propane
C3 H8
11
65.18
95.57
73.51
103.88
137.12
Benzene
C6 H6
12
73.50
103.88
81.63
112.19
149.58
Isobutene
C4 H8
12
77.09
103.88
85.68
112.19
149.58
n-Butane
C4 H10
14
89.10
120.50
97.42
128.81
174.51
Isobutane
C4 H10
14
88.52
120.50
96.84
128.81
174.51
n-Pentane
C5 H12
17
111.91
145.43
120.20
153.74
211.91
Isopentane
C5 H12
17
111.69
145.43
119.99
153.74
211.91
n-Hexane
C6 H14
20
134.78
170.36
143.06
178.67
249.30
n-Heptane
C7 H16
23
157.62
195.29
165.94
203.60
286.70
Octane
C8 H18
26
180.60
220.22
188.83
228.53
324.09
moved and the gas disperses. Spreading at the speed of light
the blackbody/thermal radiation density decreases faster than
the density of slower moving gas molecules. As the radiation density decreases, the rate at which polyatomic gaseous
molecules absorbs blackbody/thermal radiation decreases in
time. Hence their vibrational energy decreases although their
mean velocity remains constant. Now place a thermometer in the expanding wall-less gas, what will it read? Traditional kinetic theory claims that the temperature will be the
same because the gas molecule’s velocity remains constant
i.e. temperature is only associated with the system’s kinemat-
ics [2–3]. However, without walls the blackbody/thermal radiation decouples from thermal equilibrium i.e. the mean velocity of the gas molecules are associated with one temperature, but the radiation density is no longer associated with that
temperature. This bodes the question: What is the real temperature? Of course this means accepting that the thermometer not only exchanges kinetic energy with the gas molecules,
but it also exchanges blackbody/thermal radiation with its
surroundings.
The above is another reason that this author hypothesizes
that kinetic theory can falter in systems without walls. The
Kent Mayhew. A New Perspective for Kinetic Theory and Heat Capacity
169
Volume 13 (2017)
PROGRESS IN PHYSICS
Issue 3 (July)
Table 2: Engineer’s accepted adiabatic index compared to theoretical: Eqn. (14). Note: Data in first six columns after Rolle [22]. Rolle’s
reference: J.F. Masi, Trans. ASME, 76:1067 (October, 1954): National Source of Standards (U.S.) Circ. 500, Feb. 1952; Selected Values
of Properties of Hydrocarbons and Related Compounds, American Petroleum Institute Research Project 44, Thermodynamic Research
Center, Texas, A&M University, College Station, Texas.
n′′
Molar
mass
[g/mol]
Engineer’s
R
[J/kg*K)]
Engineer’s
Cp
[kJ/mol*K)]
Engineer’s
Cv
[kJ/mol*K)]
Accepted
adiabatic
index(γ)
Theoretical
index (γ)
Eqn. (14)
Substance
Helium
He
1
4.00
2079
5.196
3.117
1.67
1.67
Neon
Ne
1
20.18
412
1.030
0.618
1.67
1.67
Argon
Ar
1
39.94
208
0.521
0.312
1.67
1.67
Xenon
Xe
1
131.30
63
0.1568
0.095
1.67
1.67
Hydrogen
H2
2
2.02
4124
14.302
10.178
1.41
1.4
Nitrogen
N2
2
28.02
297
1.040
0.743
1.4
1.4
Oxygen
O2
2
32.00
260
0.917
0.657
1.4
1.4
Nitric oxide
NO
2
30.01
277
0.995
0.718
1.39
1.4
Water vapor
H2 O
3
18.02
462
1.864
1.402
1.33
1.29
Carbon dioxide
CO2
3
44.01
189
0.844
0.655
1.29
1.29
Sulfur dioxide
SO2
3
64.07
130
0.621
0.491
1.26
1.29
Ammonia
NH3
4
17.03
488
2.096
1.607
1.30
1.22
Methane
CH4
5
16.04
519
2.227
1.708
1.30
1.18
Ethylene
C2 H4
6
28.05
297
1.552
1.256
1.24
1.15
Ethane
C2 H6
8
30.07
277
1.751
1.475
1.19
1.12
Propylene
C3 H6
9
42.08
198
1.519
1.279
1.19
1.11
Propane
C3 H8
11
44.10
189
1.667
1.478
1.13
1.09
Benzene
C6 H6
12
78.11
106
1.045
0.939
1.11
1.08
Isobutene
C4 H8
12
56.11
148
1.527
1.374
1.11
1.08
n-Butane
C4 H10
14
58.12
143
1.676
1.533
1.09
1.07
Isobutane
C4 H10
14
58.12
143
1.666
1.523
1.09
1.07
n-Pentane
C5 H12
17
72.15
115
1.666
1.551
1.07
1.06
Isopentane
C5 H12
17
72.15
115
1.663
1.548
1.07
1.06
n-Hexane
C6 H14
20
86.18
96
1.660
1.564
1.06
1.05
n-Heptane
C7 H16
23
100.20
83
1.656
1.573
1.05
1.04
Octane
C8 H18
26
114.23
73
1.653
1.581
1.05
1.04
other reason kinetic theory may falter without walls is that
wall-gas interactions no longer exist, hence kinetic theory’s
complete virtues may be limited to systems with walls
[24–25] i.e. experimental systems.
body radiation has a temperature associated with it, should no
longer be ignored. In other words, even a vacuum can have
a temperature, although it has no matter and comparatively
speaking only contains a minute amount of energy.
Pressure is traditionally envisioned as being solely due to
change in translational energy i.e. “every molecule that im4 Discussion of other implications
pinges and rebounds exerts an impulse equal to the difference
This author [24–25] has hypothesized that blackbody/thermal in its momenta before and after impact” [pg. 32, 20]. Inradiation within a system has a temperature associated with terestingly, the analysis given herein does alter such explanait. So although the total energy associated with radiation of- tions just because the rotational energy plus the translational
ten is infinitesimally small in comparison to the total energy energy of the gas molecules now combine to exert pressure.
associated with the kinematics of matter, the idea that black- Moreover, consider the tennis ball impacting a wall. Ask
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Kent Mayhew. A New Perspective for Kinetic Theory and Heat Capacity
Issue 3 (July)
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Volume 13 (2017)
Fig. 3: Theoretical molar heat capacity based on our theoretical equations (12) and (13) versus empirical values, plus the traditional theoretical isometric molar heat capacity plot [based upon degrees of
freedom, equation (2)].
Fig. 4: Theoretical adiabatic index [eq. (14)] versus number of atoms (solid line). Adiabatic index data
points based upon engineering table for gases.
yourself: Are not both the rotational and translational energy of that ball exchanged with the wall. So why would
a gas molecule behave any differently? Just because wall
molecules are bound i.e. cannot rotate, does not mean that
they don’t exchange rotational energy/momentum with an impacting gas! The gas’ mean translational velocity (mv2 /2) can
no longer be simply equated in terms of Boltzmann’s constant (kT/2). This has consequences to fundaments such as
Maxwell’s velocity distributions for gases. In our analysis,
the magnitude of translational energy compared to rotational
energy is not defined beyond that they add up to and equal, the
summation of the walls molecule’s kinetic energies! Since the
gas’ total kinetic energy remains the same, then most of what
is known in quantum theorem still applies with the change
being how a gas’ kinetic energy is expressed.
Consider the hypothesis that rotational energy of a gas is
frozen out at low temperatures [26]. This is like claiming
that gas molecules never impact a wall at acute angles, when
in a cold environment. This author thinks in terms of thermal energy being energy that results in both intermolecular
and intramolecular vibrations within condensed matter. Just
consider the blackbody radiation curve for 3 K, whose peak
is located at wavelength of 1 mm. Compare this to 300 K,
where the radiation curves’ peak occurs in the infrared spec-
Kent Mayhew. A New Perspective for Kinetic Theory and Heat Capacity
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Volume 13 (2017)
PROGRESS IN PHYSICS
trum, wavelength equals 10 micrometers. Accepting that the
majority of thermal energy is in the infrared then this author
also believes that somewhere between 3 K and 300 K, a system’s thermal energy density will no longer proportional to
temperature i.e. probably aroound 100 K. Perhaps it is the
gas’ vibrational energy that is frozen out? Understandably, at
low temperatures the blackbody/thermal radiation within the
system may be such that it does not provide enough thermal
energy (infrared) for measurable gas vibration. However, this
should equally apply to the system’s walls, unless the walls
have more thermal energy relative to the gas i.e. apparatus
considerations? This is conjecture, as remains the current notion that rotational energies are frozen out.
For gases the accepted difference between molar isobaric
heat capacity and molar isometric heat capacity is the ideal
gas constant (R). Accordingly [2–3]:
C p − Cv = R.
(15)
The difference in heat capacities is obviously independent
of the type of gas. This implies that the difference depends
upon the system’s surroundings and not the experimental system, nor its contents. This fits this author’s assertion that “the
ideal gas constant is the molar ability of a gas to do work per
degree Kelvin” [27]. This is based upon the realization that
work is required by expanding systems to upwardly displace
our atmosphere’s weight, i.e. an expanding system does such
work, which becomes irreversibly lost into the surrounding
Earth’s atmosphere. The lost work being [24, 28–29]
Wlost = Patm dV.
(16)
This does not mean that the atmosphere is always upwardly displaced, rather that the energy lost by an expanding
system is defined by equation (17). This lost energy can be
associated with a potential energy increase of the atmosphere,
or a regional pressure increase. Note: A regional pressure increase will result in either a volume increase, or viscous dissipation i.e. heat created = lost work. This requires the acceptance that the atmosphere has mass and resides in a gravitational field. It is no different than realizing that an expanding
system at the bottom of an ocean, i.e. a nucleating bubble,
must displace the weight of the ocean plus atmosphere. Accordingly, any expanding system here on Earth’s surface must
expend energy/work to displace our atmosphere’s weight and
such lost work, is immediately or eventually lost into the surrounding atmosphere. Accepting this then allows one to question our understanding of entropy [24, 29].
5 Conclusions
Kinetic theory has been reconstructed with the understanding that a gas’ kinetic energy has both translational and rotational components that are obtained from the wall molecule’s
kinetic energy. Therefore, the gas’ translational plus rotational energies along each of the x, y and z-axis, are added
172
Issue 3 (July)
and equated to the wall molecules’ kinetic energy along the
identical three axes. No knowledge pertaining to the magnitudes of the gas’ rotational energy versus translational energy
is claimed. This is then added to the gas’ internal energy e.g.
vibrational energy, in order to determine the gas’ total energy.
The empirically known heat capacity and adiabatic index
for all gases are clearly a better fit to this new theory/model,
when compared to accepted theory. The fit for monatomic
through triatomic gases is exceptional, without any reliance
upon traditionally accepted exceptions! Moreover, our model
treats all polyatomic molecules in the same manner as condensed matter.
Seemingly, Lord Kelvin’s assertion that equipartition was
wrongly derived, may have been right after all. Accepting
that the traditional degrees of freedom in equipartition theory may be mathematical conjecture rather than constructive
reasoning will cause some displeasure. Certainly, one could
argue that what is said herein is really just an adjustment to
our understanding. Even so, it will alter how pressure is perceived that being due to the gas molecules’ momenta from
both rotation and translation, which is imparted onto a surface. Ditto for the consideration of a gas’ energy in quantum
theory.
The consequence of a polyatomic gas’ thermal vibrations
being related to its surrounding thermal radiation may alter
our conceptualization of temperature, i.e. a vacuum now has
a temperature. The notion that rotation in cold gases is frozen
out was also questioned. Perhaps it is a case that the thermal
energy density does not remain proportional to temperature,
as T approaches 0, which also is the case for very high temperature gases.
The difference between isobaric and isometric heat capacity is gas independent. This fits well with this author’s assertion that lost work represents the energy lost by an expanding
system into the surrounding atmosphere. Interestingly, for a
mole of gas molecules this lost work can be related to the
ideal gas constant.
To some, the combining of a gas’ rotational and translational energy may seem like a minor alteration, however the
significance to the various realms of science maybe shattering. Not only may this help put to rest more than a century of
speculations, it also may alter the way that thermodynamics
is envisioned. If accepted it actually opens the door for a simpler new thermodynamics vested in constructive logic, rather
than mathematical conjecture.
A thanks goes out to Chifu E. Ndikilar for his helpful preliminary comments, as well as both Dmitri Rabounski and
Andreas Ries for their insights in finalizing the paper.
6 Example calculations
1. Table 1 for n′′ = 3; our theoretical values:
[equation (12)]: I.e. Cv = 72 R = 72 8.31 J/(mol*K)
= 29.09 J/(mol*K).
Kent Mayhew. A New Perspective for Kinetic Theory and Heat Capacity
Issue 3 (July)
PROGRESS IN PHYSICS
[eq. (13)]: I.e. C p = 29 R = 92 8.31 J/(mol*K)
= 37.40 J/(mol*K).
For n′′ =3, traditional accepted theoretical value is equation (2): I.e. Cv = 92 R = 92 8.31 J/(mol*K)
= 37.40 J/(mol*K).
2. Table 2, for n′′ = 3. Accepted adiabatic index (γ) for
carbon dioxide (n′′ = 3) based upon engineering data
[22] is γ = 0.844/0.655 = 1.29. Our theoretical adiabatic index (γ) is equation (14): I.e.
γ=
9
2
7
2
Volume 13 (2017)
12. Thomson W. (1904). Baltimore Lectures. Baltimore: Johns Hopkins
University Press. Sec. 27. Re-issued in 1987 by MIT Press as Kelvin’s
Baltimore Lectures and Modern Theoretical Physics: Historical and
Philosophical Perspectives. (Robert Kargon and Peter Achinstein, editors).
13. Rayleigh J.W.S. The Law of Partition of Kinetic Energy. Phil. Mag.,
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14. Pais A. Subtle is the Lord. Oxford University Press. Oxford UK 1982.
15. Hermann Armin (1971). The Genesis of Quantum Theory (1899–1913)
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16. Masi J.F., Petkof B. J. Res. Natl. Bur. Stand., 1952, v. 48(3), 179–187.
= 1.29.
Submitted on June 16, 2017
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