Hydrogen critical constants

Use the critical constants for hydrogen given in Table 5.3 to calculate the parameters a and b for the van der Waals and Redlich-Kwong equations for hydrogen. Use each of these equations to calculate the compressibility factor z for hydrogen as a function of l/Vm at 50 K between 0.1 Mpa and 20 MP, and compare your calculated values with the experimental values of Johnston and White [16]. 

If the gas is either hydrogen or helium, determine adjusted critical constants from the empirical formulas... 

White, Friedman, and Johnston (343) have measured the critical constants for normal hydrogen and have found 33.244 K. and 12.797 atmospheres. Woolley, Scott, and Brickwedde have presented data on the dissociation energy and the thermodynamic properties for the ideal diatomic gas, including contributions from nuclear spin. We have omitted the spin entropy in compiling our tables. Thermodynamic properties for the ideal monatomic gas have been computed at the National Bureau of Standards (395). Note that the reference state represents 2 gram atomic weights for this element. 

It has been our experience that 7s(r) and Vs(r) play different but complementary roles with respect to molecular reactivity [71,83-85], Vs(r) is effective for treating noncova-lent interactions, which are primarily electrostatic in nature [74,86-89], For instance, a variety of condensed-phase physical properties - boiling points, critical constants, heats of phase transitions, solubilities and solvation energies, partition coefficients, surface tensions, viscosities, diffusion constants and densities - can be expressed quantitatively in terms of one or more key features of Vs(r), such as its maximum and minimum, average deviation, positive and negative variances, etc. [80,90-92], Hydrogen bond donating... 

The pseudo-critical values were tested, with 0, 6 and set equal to unity, by comparison of predicted compressibility factors with the experimentally determined values for hydrogen and methane mixtures. The value of a was taken from a correlation developed earlier for high temperature systems [7] shown in Table V. The only pure reference substances available with known compressibility factors were methane, hydrogen and deuterium. The critical constants used for these gases are given in Table IV. 

These plots give good agreement with the experimental data for most vapors with the exception of hydrogen and helium, both of which have low critical temperatures and pressures. It has been found possible to use the plot for these two gases by using modified critical constants. However, neither gas is particularly important in vapor-liquid equilibria. 

The triple points, boiling points, and critical constants for the isotopic forms of hydrogen and for several ortho-para concentrations are given in Table 2.4, and vapor pressure values are shown in Table 2,5. The vapor pressure equations of Table 2.5 agree with the experimental data for hydrogen to within the experimental error over most of the liquid range to the critical point. The values for deuterium and hydrogen deuteride should not be used at pressures much above atmospheric. 

Properties of Light and Heavy Hydrogen. Vapor pressures from the triple point to the critical point for hydrogen, deuterium, tritium, and the various diatomic combinations are Hsted in Table 1 (15). Data are presented for the equiUbrium and normal states. The equiUbrium state for these substances is the low temperature ortho—para composition existing at 20.39 K, the normal boiling point of normal hydrogen. The normal state is the high (above 200 K) temperature ortho—para composition, which remains essentially constant. 

Isotopic Exchange Reactions. Exchange reactions between the isotopes of hydrogen are well known and well substantiated. The equihbrium constants for exchange between the various hydrogen molecular species have been documented (18). Kinetics of the radiation-induced exchange reactions of hydrogen, deuterium, and tritium have been critically and authoritatively reviewed (31). The reaction T2 + H2 — 2HT equiUbrates at room temperature even without a catalyst (30). 

The critical hydrogen content for the ductility loss increased with increasing hydrogen solubility in the alloy. The fracture surfaces were not characteristic of those found under conditions of SCC. In terms of hydrogen and deuterium solubility in a similar series of bcc alloys, the equilibrium constants were determined at infinite dilution as a function of temperature The free energy function was expressed in terms of the bound-proton model. 

Bockris and Subramanyan during studies of the permeation of hydrogen through pure Fe and Fe-SNi alloy found that a normal permeation transient was obtained (Fig. 20.21), providing the overpotential was less than a critical value, and when the overpotential was less than it was possible to reproduce the normal permeation curve, i.e. apply the polarising current at a constant rj < t , allow J to attain a steady value, switch off, reapply... 

This hypothesis has been criticized by Busvine (2,3), Domenjoz (10), Muller (18), and Cahn (4). Domenjoz and Muller have shown that there is no direct correlation between activity toward a variety of insects in a number of compounds of the type Ar2CHCCl3 and the amount of hydrogen chloride liberated under standard conditions. Busvine attempte( 1 a correlation for similar compounds between activity toward lice and bedbugs and this author s reaction-rate constants (2, 5) for second-order elimination with ethanolic alkali and found that no statistically significant correlation exists. 

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