Ammonia diffusion

Ammonia gas is diffusing at a constant rate through a layer of stagnant air 1 mm thick. Conditions are such that the gas contains 50 per cent by volume ammonia at one boundary of the stagnant layer. The ammonia diffusing to the other boundary is quickly absorbed and the concentration is negligible at that plane. The temperature is 295 K and the pressure atmospheric, and under these conditions the diffusivity of ammonia in air is 1.8 x 10 5 m2/s. Estimate the rate of diffusion of ammonia through the layer. 

Table 7.3. Relative Fluorescence Quantum Yield of Crystal Violet,

Therefore, the ISE potential depends on the CO2 partial pressure with Nernstian slope. Contemporary microporous hydrophobic membranes permitted the construction of a number of gas probes, developed mainly by the Orion Research Company (for a survey see [143]. The most important among these sensors is the ammonia electrode, in which ammonia diffusing through the membrane affects the pH at a glass electrode. Other electrodes based on similar principles respond to SO2, HCN, H2S (with an internal S ISE), etc. The ammonia probe has a better detection limit than the ammonium ion ISE based on the non-actin ionophore. The response time of gas probes depends mostly on the rate of diffusion of the test gas through the microporous medium [77,143]. 

A further disadvantage of the Conway method is that the volume of solution in the center well is critical and must be pipetted with volumetric precision as well as dispatch. The Conway dishes must be prepared considerably in advance of their use, for the danger of contamination becomes excessive if they are prepared at the bedside. The Seligson technique requires no quantitative measurements except for the volume of the unknown specimen, since the ammonia diffused is concentrated in a very small volume, all of which is transferred by dipping it into the colorimeter tube. The volume of acid which coats the diffusion rod is... 

Holmes, R.M., McClelland, J.W., Sigman, D.M., Fry, B., and Peterson, B.J. (1998) Measuring 15N-NH4+ in marine, estuarine and fresh waters an adaptation of the ammonia diffusion method for samples with low ammonium concentrations. Mar. Chem. 60, 235-243. 

In aquatic animals, ammonia diffuses out of the body through the skin, but land animals excrete excess ammonia either as urea or uric acid. Ammonia is excreted by humans on high meat diets as a strategy to conserve Na+ and K +. Excess PO4- and SO4- produced from phosphoproteins and S-containing amino acids are excreted as ammonium salts Na+ and K+ are exchanged for NH in the kidney. The excretion of urea requires a plentiful supply of water, as it is normally excreted in solution, whereas uric acid is very insoluble and is excreted as a solid by birds and reptiles. Thus, in animals in which weight, or the conservation of water, is important (e.g., birds), excess ammonia is excreted as uric acid. 

For the particle sizes used in industrial reactors (> 1.5 mm), intraparticle transport of the reactants and ammonia to and from the active inner catalyst surface may be slower than the intrinsic reaction rate and therefore cannot be neglected. The overall reaction can in this way be considerably limited by ammonia diffusion through the pores within the catalysts [211]. The ratio of the actual reaction rate to the intrinsic reaction rate (absence of mass transport restriction) has been termed as pore effectiveness factor E. This is often used as a correction factor for the rate equation constants in the engineering design of ammonia converters. 

Two effects cause the low production capacity of coarse-grained catalyst first, large grain size retards transport of the ammonia from the particle interior into the bulk gas stream, because this proceeds only by slow diffusion through the pore system. Slow ammonia diffusion inhibits the rate of reaction. At the high reaction rate typical for the converter inlet layer, only a surface layer of the catalyst grains, about 1-2 mm thick, participates in the reaction. 

Sigman, D. M., Altabet, M. A., Michener, R., McCorkle, D. C., Fry, B., and Holmes, R. M. (1997). Natural abundance-level measurement of the nitrogen isotopic composition of oceanic nitrate An adoption of the ammonia diffusion method. Mar. Chem. 57, 227—242. 

Ammonia is produced by deamination of glutamine, glutamate, other amino acids, and adenylate. A considerable quantity is derived from intestinal bacterial enzymes acting on urea and other nitrogenous eompounds. The urea comes from body fluids that diffuse into the intestine, and the other nitrogenous products are derived from intestinal metabolism (e.g., glutamine) and ingested protein. The ammonia diffuses across the intestinal mucosa to the portal blood and is eonverted to urea in the liver. 

Because the ammonia diffuses 2.04 times as fast, the chlorine will take 2.04 times as long to get there ... 

The material is known to retain its macroscopic shape during the ab-/ desorption of ammonia (Fig. 19.3), which implies an ab-/desorption mechanism where ammonia diffuses into the bulk and takes the system stepwise through (a) (b) (c) (d) in Fig. 19.7 and vice versa. For this to occur readily. 

The binary diffusivities are the same as for Example 1.11. However, in this case, only the ammonia diffuses toward the liquid interphase, since neither nitrogen nor hydrogen are soluble in the sulfuric acid solution. Therefore, equation (1-60) applies. Calculate the mole fractions of nitrogen (2) and hydrogen (3) on an ammonia (l)-free base from equation (1-61) ... 

Consider steady-state, one-dimensional diffusion of A through nondiffusing B. This might occur, for example, if ammonia (A) is absorbed from air (B) into water. In the gas phase, since air does not dissolve appreciably in water, and neglecting the evaporation of water, only the ammonia diffuses. Thus, Ng - 0, NA = constant, and... 

Ammonia diffusion from small pool to large pool... 

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