Specific heat of hydrogen

This result is independently verified by Dennison (17) who has recently given a satisfactory theory of the specific heat of hydrogen. The observed specific heat as interpreted by Dennison requires that I0 be equal to 0.464 X 10 40 g. cm.2. The very recent measurements by Cornish and Eastman (18) of the specific heat of hydrogen from the velocity of sound are said to agree very well with Dennison s theory if I0 be given the value of 0.475 X 10-40 g. cm.2. 

This may be done by considering the falling off in the specific heat of hydrogen at low temperatures. 

The specific heat of hydrogen is much higher than that of gasoline or diesel fuel, but because hydrogen is so light, the net effect is essentially negligible. The... 

For the purpose of this study of the ratio of the specific heats of hydrogen the Lummer and Pringsheim method has been adapted to a one liter flask with a precision comparable with the. extreme precision it has given in large carboys. The method consists essentially in obtaining y from observation of the cooling consequent upon small adiabatic expansions by way of the ideal gas equation... 

At 16° C. the specific heat of hydrogen at constant volume is 4 875.2 The mean value of the specific heat between 0° C. and 2350° C. has been proved by Pier8 to be given by the expression 4-700+4 5X 10-4Z. For the specific heat at constant pressure Lewis and Randall4 give the expression CJ)=4-50+0-0009T. 

Values given for gases ai y to such substances as air, nitrogen, carbon dioxide, light hydrocarbon mixtures (no condensation), ttc. Because of die hi diermal cwductivides and specific heats of hydrogen and helhim, gas... 

According to Regnault, the mean specific heat of hydrogen, under atmospheric pressure, has the same value between 0 and 200 as between —30° and +110°. 

In the meantime Bonhoeffer and Harteck were looking for the two mysterious modifications of hydrogen, the existence of which was predicted by the quantum theory on the basis of a curious decline of the specific heat of hydrogen at low temperatures and of the intensity variations of a series of lines in the molecular spectrum of hydrogen. 

This factor cannot be connected with permanent structural capacities or disabilities of molecules, since the operation or non-operation of degrees of freedom depends upon the temperature. At low temperatures the specific heat of hydrogen falls from 5 to 3, and that of metals drops to zero. Fig. 12 illustrates the behaviour of hydrogen, Fig. 13, that of some typical soMs, and Fig. 14 shows the ideal course of the complete curve for a diatomic molecule. 

But it is not only the number of the solutions which matters their character assumes predominant importance in some problems, and this in various peculiar ways which, however, it is only expedient to introduce as the interpretation of experimental facts demands. One concrete example arises from certain of the facts already considered. The necessity for the quantum theory itself emerges clearly from the failure of the kinetic theory to provide without it an adequate description of the energy content of matter. The need for further postulates is shown by the failure of the ideas so far introduced to account adequately for the detailed behaviour of the specific heat of hydrogen. 

The problem which had to be left unsolved at an earlier stage can now be dealt with. The mode of variation with temperature of the rotational component of the specific heat of hydrogen indicated clearly that hydrogen molecules are divisible into two well-defined groups, those with even numbers of rotational quanta and those with odd numbers. In the light of what has just been discussed there seems... 

Cp = specific heat of hydrogen, 14.307 J/g-K riio ij, = mass flow rate of oxygen inlet, g/s... 

During the 3 years after the doctorate. Van Vleck s research was on atomic physics. He worked on the theory of the specific heat of hydrogen and wrote a paper on the correspondence principle for absorption. His expertise in this area accounts for his selection to prepare the National Research Coimcil report on the quantum theory of line spectra. After the advent of quantum mechanics. Van Vleck s research concentrated on the theory of magnetism. In 1932, he published the Theory of Electric and Magnetic Susceptibilities (Fellows 1985). His subsequent research opened the way to much of what is now called "magnetochemistry" and "ligand field chemistry."... 

The treatment of the latter appears important for the following reason. As shown in II, there exist molecules with two nuclei, where both term systems, the one symmetric and the one anti-symmetric in the nuclei appear (for instance N2 and Nj ) If we can trust the empirically measured specific heat of hydrogen, this is also the case for H2. For a closer investigation of the properties of the hydrogen nucleus that are hidden behind this fact, one can consider the molecules H2O, NH3 and CH4. As will be shown, only very subtle properties of the spectra or specific heats of these substances can provide the information and the present measurements are not sufficient for a decision. 

Plot the relationships for molar specific heat of hydrogen, air, and water vapor given in Eqs. (3.24), (3.27), and (3.28), respectively. Over what temf>erature would you estimate that you can consider the specific heats constant ... 

Gearhart, Hydrogen] Gearhart, Clayton Astonishing Successes and Bitter Disappointment . The Specific Heat of Hydrogen in Quantum Theory, Archive for the History of Exact Sciences 64 (2010), p. 113-202. 

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