Carbon Dioxide-Water Equilibrium

On dissolution, C02 hydrolyzes that is, a molecule of carbon dioxide combines with a water molecule to form one molecule of C02 H20. C02 (aq) and C02 H20 are alternative notations for the same chemical species corresponding to A(aq) in (7.2). Dissolved carbon dioxide, C02 H20, dissociates twice to form the carbonate and bicarbonate ions  

Note that liquid water concentration has already been incorporated into the hydrolysis constant and that Khc is identical to the Henry s law coefficient for carbon dioxide, Wco2- 

Noting the similarity of this expression to Henry s law, we can define the effective Henry s law constant for CO2, // 02, as 

The effective Henry s law constant always exceeds the Henry s law constant 

Let us assume momentarily that the atmosphere contains only C02 and water. What is the pH of cloud and rainwater in this system Use an ambient mixing ratio of 350 ppm and a temperature of 298 K. The concentrations of the ions in solution will satisfy the electroneutrality equation 

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Carbon Dioxide/Water Equilibrium 345 Sulfur Dioxide 348 Ammonia/Water Equilibrium 353 Nitric Acid/Water Equilibrium 355 Equilibrium of Other Important Atmospheric Gases Aqueous-Phase Reaction Rates 361 S(IV) to S(VI) Transformation and Sulfur Chemistry 363... 

Examples 13.8 and 13.9 treat the carbon dioxide water equilibrium. The corresponding problem for SO2 is of paramount importance in air pollution control [ 16]. The corresponding reactions seem to be... 

Table 21.22 Saturated solubilities of atmospheric gases in sea-water at various temperatures Concentrations of oxygen, nitrogen and carbon dioxide in equilibrium with 1 atm (lOI 325 N m ) of designated gas...

Figure 6-6 also shows the variation in the partial pressure of carbon dioxide in equilibrium with the lagoon s waters. The average value of this pressure exceeds the atmospheric value, 1, so on average, carbon dioxide is evaporating from the lagoon. The evaporation rate is greatest at times of maximum alkalinity and bicarbonate concentration and minimum carbonate ion concentration. 

Figure 6-8 shows how the partial pressure of carbon dioxide in equilibrium with surface water oscillates in phase with the fluctuations in precipitation rate, saturation state, and temperature. The oscillations in alkalinity and bicarbonate concentrations have shifted in phase by about 90° because these quantities decrease when precipitation and evaporation are removing carbon from the system at above-average rates. 

Assuming that nitroguanidine explodes to produce carbon dioxide, water, carbon monoxide, hydrogen, and nitrogen,21 assuming that the equilibrium constant for the reaction, CO + H20 C02 + H2, is 6, and that the molecular heat of formation at con-... 

The most productive two-phase (H-V or H-Lhc) equilibrium apparatus was developed by Kobayashi and coworkers. The same apparatus has been used for two-phase systems such as methane + water (Sloan et al., 1976 Aoyagi and Kobayashi, 1978), methane + propane + water (Song and Kobayashi, 1982), and carbon dioxide + water (Song and Kobayashi, 1987). The basic apparatus described in Section 6.1.1.2 was used in a unique way for two-phase studies. With two-phase measurements, excess gas was used to convert all of the water to hydrate at a three-phase (Lw-H-V) line before the conditions were changed to temperature and pressures in the two-phase region. This requires very careful conditioning of the hydrate phase to prevent metastability and occlusion. Kobayashi and coworkers equilibrated the hydrate phase by using the ball-mill apparatus to convert any excess water to hydrate. 

The pH-buffering of extracellular fluid depends in part on the carbon dioxide/ bicarbonate equilibrium so that the intake of sodium bicarbonate is followed by a brief alkalosis and an increased excretion of sodium carbonate in the urine. Depending on its carbonate concentration, the pH of the urine may rise to 8.07. Large doses (80—100 g/day) of sodium bicarbonate were needed if the pH of stomach contents was to be maintained at 4 or over in patients with duodenal ulcers8. Oxidation of organic anions in the body to carbon dioxide and water permits the use of sodium citrate, lactate or tartrate instead of sodium bicarbonate. In an analogous manner the ingestion of ammonium chloride induces a brief acidosis as a result of the metabolic conversion of ammonia to urea and lowers the pH of the urine. 

When dissolved in a solvent, some solutes combine with the solvent to form solvated species. The two outstanding examples in aqueous solution are carbon dioxide to form COz(aq) (carbonic acid) and ammonia to form NH3(aq) (ammonium hydroxide). In many cases the equilibrium constant for the reaction is unknown or not known with sufficient accuracy for thermodynamic purposes. Conventions have been established for treating such systems thermodynamically. Here we discuss the carbon dioxide-water... 

The equilibrium limitations of these two reforming reactions are overcome by continuous removal of hydrogen and carbon monoxide which are directly oxidized electrochemically at the anodic electrode. There, these components react with carbonate ions from the electrolyte to produce carbon dioxide, water and electrons according to the following stoichiometric relationships ... 

The qualitative phase behaviour of the carbon dioxide-water-1-propanol system is discussed for the temperatures 303 and 333 K in Figure 1, where isothermal Gibbs phase diagrams are arranged in prisms to show the influence of pressure on phase equilibrium. 

Figure 4. Three-phase equilibrium LtL2V in the system carbon dioxide-water-1-propanol at 333 K and 13.1 MPa exp., this work — Calculated with Peng-Robinson EOS using Panagiotopoulos and Reid mixing rule, left side prediction from pure component and binary data alone, right side interaction parameters fitted to ternary three-phase equilibria at temperatures between 303 and 333 K...

The hydrate and phenol clathrate equilibrium data of the water-carbon dioxide, phenol-carbon dioxide, and water-phenol-carbon dioxide systems are presented in Table 1 and depicted in Figure 2. In order to establish the validity of the experimental apparatus and procedure the hydrate dissociation pressures of carbon dioxide measured in this work were compared with the data available in the literature (Deaton and Frost [7], Adisasmito et al. [8]) and found that both were in good agreement. For the phenol-carbon dioxide clathrate equilibrium results, as seen in Figure 2, the dramatic increase of the dissociation pressures in the vicinity of 319.0 K was observed. It was also found in the previous study (Kang et al. [9]) that the experimental phenol-rich liquid-phenol clathrate-vapor (Lp-C-V) equilibrium line of the binary phenol-carbon dioxide system could be well extended to the phenol clathrate-solid phenol-vapor (C-Sp-V) equilibrium line (Nikitin and Kovalskaya [10]). It is thus interesting to note that a quadruple point at which four individual phases of phenol-rich liquid, phenol clathrate, solid... 

For the ternary water-phenol-carbon dioxide system, several interesting phenomena were observed. As shown in Figure 2, the four-phase, water-rich liquid-phenol-rich liquid-phenol clathrate-vapor (Lw-Lp-C-V), dissociation pressures were measured at several temperatures near 293.0 K. Like above the phenol-carbon dioxide clathrate equilibrium results, the dramatic increase of the four-phase dissociation pressures was observed in a vicinity of 293.0 K. One of the most interesting results observed in this work is that a quintuple point at which the five phases of water-rich liquid, phenol-rich liquid, carbon dioxide-rich liquid, phenol clathrate, and vapor coexist in equilibrium was carefully measured and found to be 293.7 K and 57.2 bar. 

Table 6 Isothermal Vapor-Liquid Equilibrium results for Carbon dioxide - Water...

Bamberger, A.G. Sieder, and G. Maurer. 2000. High-pressure (vapor + liquid) equilibrium in binary mixtures of (carbon dioxide + water or acetic acid) at temperatures from 313 to 353 K. /. Supercrit. Fluids 17 97-110. 

Addition of a solute to the aqueous phase changes the D/H and 180/16Q ratios in the free water since newly formed hydration spheres selectively take hydrogen and oxygen isotopes. This in turn results in the change in the D/H and 0/" 0 ratios in the water vapor or the 0/ 0 ratio in the carbon dioxide in equilibrium with the free water, which is considered to have an energy state similar to pure water. 

A large excess of carbon dioxide is required because caffeine does not dissolve to its (neat) solubility limit during the extraction of coffee beans. Instead, the concentration achieved in the carbon dioxide phase is governed by an equilibrium interaction that is present in the carbon dioxide-caffeine-coffee system (or, more precisely, the carbon dioxide-water-caffeine-coffee system). The measured equilibrium isotherm for the system is given in figure 10.2... 

The addition of water to carbon dioxide, CO2 + H2O OC(OH)2 H +HCOJ, is formally very similar to its addition to aldehydes and ketones, although here only 0.2% of the carbon dioxide is hydrated at equilibrium, and observations make use of the further equilibrium with and HCO3. A summary of work up to 1958 has been given by Edsall and Wyman,and several later kinetic studies have been made " the hydration process shows general catalysis by basic anions. It is particularly interesting that the enzyme carbonic anhydrase, which is active in maintaining the carbon dioxide-bicarbonate equilibrium in the body, is also an effective catalyst for the hydration of acetaldehyde and other carbonyl compounds. ... 

Section 19 9 Carbon dioxide and carbonic acid are m equilibrium m water Carbon dioxide IS the major component... 

Cement mortar will be attacked by waters that have an excess of free carbon dioxide compared with that of waters that are in a lime-carbonic acid equilibrium. There is a two-step mechanism with a carbonization process according to... 

The most important property of the dissolved solids in fresh waters is whether or not they are such as to lead to the deposition of a protective film on the steel that will impede rusting. This is determined mainly by the amount of carbon dioxide dissolved in the water, so that the equilibrium between calcium carbonate, calcium bicarbonate and carbon dioxide, which has been studied by Tillmans and Heublein and others, is of fundamental significance. Since hard waters are more likely to deposit a protective calcareous scale than soft waters, they tend as a class to be less aggressive than these indeed, soft waters can often be rendered less corrosive by the simple expedient of treating them with lime (Section 2.3). 

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