Hydrogen molecular speed

At room temperature, the usual range of molecular speeds is 300 to 500 m/s. Hydrogen is unusual because of its low mass its rms speed is about 1900 m/s. 

Under true superpermeable hydrogen flux conditions, the large numbers of molecules predicted to impact upon a membrane surface follow, in part, as a consequence of the very high molecular speeds of gas phase hydrogen relative to the size of reactor vessels. For example, the mean velocity of a hydrogen molecule, H2, in the gas phase at 273 K (0 °C) is 1.7 km s [8]. Mean molecular velocity increases in proportion to the square root of the absolute temperature. In a chemical reactor at 673 K (400 °C), for example, the mean velocity of H2 will increase by a factor of (673 K/273 K) / from 1.7 km s at 273 K to 2.7 km s at 673 K. Mean molecular velocity decreases inversely with the square root of the molecular mass. For deuterium molecules, D2, with a molecular mass approximately twice that of H2, the mean molecular velocity is less than that of H2 by a factor of 2 /, approximately 1.2 km s at 273 K (0 °C) [8]. 

Neither of the two types of chain termination reactions mentioned above in the isotopic hydrogen example is a fast reaction by these standards. Heterogeneous removal of chain centres requires as a minimum their delivery to a phase boundary, and at typical molecular speeds near 10 cm sec quite small apparatus dimensions would be necessary to yield a 10 sec reaction rate even under high vacuum conditions. This argument can be extended to the general observation that heterogeneous steps play no direct part in the interior of the shortlived experiments in shock tubes. 

Figure 5.9 Relation of molecular speed to molar mass. When ammonia gas, which is injected into the left arm of the tube, comes in contact with hydrogen chloride, which is injected into the right arm of the tube, they react to form solid ammonium chloride NHsCg) + HCI(g) — NH4CI(s). Because NH3 (MM = 17 g/mol) moves faster than HCI (MM = 36.5 g/mol), the ammonium chloride forms closer to the HCI end of the tube.

The main area of interest for plasticizers in PET is in the area of dyeing. Due to its lack of hydrogen bonds PET is relatively difficult to dye. Plasticizers used in this process can increase the speed and intensity of the dyeing process. The compounds used, however, tend to be of low molecular weight since high volatiHty is required to enable rapid removal of plasticizer from the product (see Dye carriers). 

High gas yield shows up as higher speed on the compressor (if centrifugal). In many cases, lower molecular weight (due to higher hydrogen content) can have the same effect. 

A pattern emerges when this molecular beam experiment is repeated for various gases at a common temperature Molecules with small masses move faster than those with large masses. Figure 5 shows this for H2, CH4, and CO2. Of these molecules, H2 has the smallest mass and CO2 the largest. The vertical line drawn for each gas shows the speed at which the distribution reaches its maximum height. More molecules have this speed than any other, so this is the most probable speed for molecules of that gas. The most probable speed for a molecule of hydrogen at 300 K is 1.57 X 10 m/s, which is 3.41 X 10 mi/hr. 

In pseudoplastic substances shear thinning depends mainly on the particle or molecular orientation or alignement in the direction of flow, this orientation is lost or regained at the same speed. Additionally many dispersions show this potential for particle or molecule interactions, this leads to bonds creating a three-dimensional network structure. They are often build-up from relatively weak hydrogen or ionic bonds. When the network is disturbed. 

Fig. 5.44 The voltammogram of molecular hydrogen at a rotating bright platinum disk electrode in 0.5 m H2S04, pHl = 105 Pa, 25°C. The rotation speed

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