Atmospheric carbon dioxide equilibrium with

The radiocarbon ratio also evolves very rapidly from its initial value of -50 to an average value of about -8 per mil. This evolution is not a consequence of evaporative concentration but, instead, of an approach to equilibrium with atmospheric carbon dioxide. Average surface seawater contains significantly less radiocarbon than does the atmosphere because its isotopic composition is affected by exchange with the deep ocean as... 

The most actively cycled reservoir of carbon is atmospheric C02 (it constitutes 0.034% of the atmosphere). Carbon dioxide dissolves readily in water and is in direct equilibrium with dissolved inorganic forms of carbon (H2C03, HCO, and CO7-, see Section 6.2.1.3). Once there, it may precipitate as solid calcium carbonate (limestone). Corals and algae encourage this reaction and build up limestone reefs in the process, but a much larger portion in the deep sea equilibrates only at the slow rate of... 

Vinogradov has pointed out that with the appearance of the biosphere somewhere on the verge of 3-10 yr ago, there was a major upheaval in the evolution of the Earth. Oxidizing processes were abruptly accelerated, a nitrogen atmosphere arose in which carbon dioxide predominated over methane, and free carbon was oxidized to CO2. After the carbon was oxidized or at the same time as that process, there began oxidation of divalent iron (at — 10 ), which led to subsequent wholesale deposition of the sediments of the Precambrian BIF. Free carbon in equilibrium with the atmosphere appeared only after complete oxidation of ferrous iron compounds in the hydrosphere and on the land surface. 

Figure 26-18 shows the carbon cycle. Carbon dioxide in the atmosphere is in equilibrium with an enormous quantity that is dissolved in oceans, lakes, and streams. Some of this dissolved CO2 was once in the form of calcium carbonate (CaC03), the main component of the shells of ancient marine animals. The shells were eventually converted into limestone, which represents a large store of carbon on Earth. When the limestone was exposed to the atmosphere by receding seas, it weathered under the action of rain and surface water, producing carbon dioxide. Some of this CO2 was released into the atmosphere. This process continues today. 

A river has a pH of approximately 6. If the river water is in equilibrium with atmospheric carbon dioxide (which has a pressure, Pcc,2, °f approximately 10-3 5 atm), what are the concentrations of carbonate system species in the water ... 

Distilled water. Distilled water in equilibrium with air contains a small amount of atmospheric carbon dioxide and has therefore an acid reaction. Normal air contains approximately 0.03 volume per cent of carbon dioxide. The distribution coeffi-... 

Other natural soil acidifying agents are found in the atmosphere. Carbon dioxide has a concentration of only 350 parts per million (by volume) in the open atmosphere, so that rainwater in equilibrium with this air is a very dilute solution of carbonic acid (10 M). This source of H2CO3 is of much less consequence than the carbonic acid generated from biological activity within soils. Lightning can oxidize atmospheric nitrogen, N2, to produce NO which further oxidizes to nitric acid ... 

As in the case of calcite, the activities of various dissolved species have been calculated at different pH values for other minerals using the relevant chemical equilibria and stoichiometric restrictions. The distribution of the activities of dissolved species of hydroxy apatite is given in Figs. 3.5a and 3.5b for open and closed systems, respectively. If the system is brought to equilibrium with atmospheric carbon dioxide, the distribution will follow that shown in Fig. 3.5a. For the closed system, Ca species are the most predominant... 

As pH rises, the total amount of dissolved carbonate as [C02(aq), carbon dioxide] + [H2C03(aq), carbonic acid] + [HC03 (aq), bicarbonate] +[C03 (aq), carbonate] in equilibrium with the atmosphere increases. As before, the atmosphere is an inexhaustible reservoir of C02(g), maintaining its pressure at 3.0 x 10 atm (Figure 5). 

Present an example of a calculation of surface water pH under equilibrium with atmospheric carbon dioxide. 

In addition to the biological factors noted above, the isotopic composition of inorganic carbon is influenced by the exchange of carbon between surface waters and the atmosphere. Carbon isotopes are fractionated with the transfer of carbon between water and the atmosphere (Siegenthaler and Munnich 1981 Zhang et al. 1995), with equilibrium fractionation resulting in atmospheric carbon dioxide about 8%o depleted relative to the ocean. This effect is temperature dependent, with a change in fractionation of approximately -0.1%o per K (Mook 1986). Thus, at equilibrium, DIC in colder waters is enriched in C relative to warmer waters. In natural waters, the time required for isotopic equilibration is slow relative to the residence time of carbon in surface waters... 

Reaction with carbon dioxide. The increase in solubility of limestones in the presence of carbon dioxide is due to reversible chemical reaction (3.1) and (3.2), which form calcium and magnesium bicarbonates. For example, at 20 °C approximately 30 mg/1 of calcite will dissolve in distilled water at equilibrium with the atmospheric carbon dioxide [3.9]. 

The carbon dioxide (physically) dissolved in water - we denote it as C02 aq) -is in equilibrium with gaseous atmospheric carbon dioxide C02(g). There is no way to separate non-ionic dissolved C02 aq) and H2CO3 therefore, it is often lumped into C02 aq). Analytically, DIC can be measured by acidifying the water sample, extracting the CO2 gas produced and measuring. The marine carbonate system represents the largest carbon pool in the atmosphere, biosphere and ocean, meaning it is of primary importance for the partition of atmospheric excess carbon dioxide produced by human activity. 

The error in [h ] calculated by equation 6 is determined by the uncertainty in the known major ion concentrations and the validity of the assumptions. The assumptions about trace ion concentrations and equilibrium with atmospheric carbon dioxide probably give errors that are small. The uncertainty in the major ion concentrations can have a large effect on calculated pH values around 5.65 due to small differences in the relatively large charge concentrations when the alkalinity and acidity are near zero(5). 

The conductivity balance can also be used to estimate the pH from known major ion concentrations and measured specific conductance. By assuming equilibrium with atmospheric carbon dioxide and th trace ion contribution to the conductivity to be insignificant,... 

As an example of an acid-base equilibrium problem, consider water in equilibrium with atmospheric carbon dioxide. The value of [COj (aq)] in water at 25°C in equilibrium with air that is 390 parts per million COj (close to the concentration of this gas in the atmosphere) is 1.277 X 10 mol/L. The carbon dioxide dissociates partially in water to produce equal concentrations of H+ and HCO3" ... 

Carbon dioxide in the atmosphere is in equilibrium with carbon dioxide dissolved in the seas, most of which was once in the form of calcium carbonate, the main component of shells. Over time, calcium carbonate becomes limestone. When limestone is exposed to the atmosphere, it may weather and release CO2. 

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...

Carbon-14 (C-14) with a half-life of 5730 years decays to nitrogen-14 (N-14). A sample of carbon dioxide containing carbon in the form of C-14 only is sealed in a vessel at 1.00-atmosphere pressure. Over time, the CO2 becomes NO2 through the radioactive decay process. The following equilibrium is established ... 

It is necessary to draw attention to the variable pH of water which may be encountered in quantitative analysis. Water in equilibrium with the normal atmosphere which contains 0.03 per cent by volume of carbon dioxide has a pH of about 5.7 very carefully prepared conductivity water has a pH close to 7 water saturated with carbon dioxide under a pressure of one atmosphere has a pH of about 3.7 at 25 °C. The analyst may therefore be dealing, according to the conditions that prevail in the laboratory, with water having a pH between the two extremes pH 3.7 and pH 7. Hence for indicators which show their alkaline colours at pH values above 4.5, the effect of carbon dioxide introduced during a titration, either from the atmosphere or from the titrating solutions, must be seriously considered. This subject is discussed again later (Section 10.12). 

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. 

Solid carbon reacts with carbon dioxide gas to produce carbon monoxide. At 1,500°C, the reaction is found to be at equilibrium with a Kp value of 0.50 and a total pressure of 3.5 atm. What is the proper expression for the partial pressure (in atmospheres) of the carbon dioxide ... 

Most climate models show a climate in stable equilibrium. If the 1900 condition of 300 parts per million doubles to 600 ppm, most three-dimensional models indicate an equilibrium with an average surface temperature warming of 3.5° to 5°C (5.6° to 9°F). If the carbon dioxide content of the atmosphere doubled in one month, the earth s temperature would not reach its new equilibrium value for a century or more. 

The rate of growth of the trees slows as the forest reaches maturity and canopy closure occurs. In addition, the forest eventually establishes equilibrium with the environment, where the rate of carbon sequestration is exactly balanced by the loss of carbon dioxide to the atmosphere due to decay of dead trees and other biomass. 

Even if equilibrium had been achieved before the water mass sank, the observed water mass concentrations could exhibit apparent deviations from equilibrium, if the atmospheric pressures have changed or if the water mass temperature has been altered. Thus, deepwater that was last at the sea surface hundreds of years ago could potentially have equilibrated with the atmosphere at much different partial pressures of gases such as methane and carbon dioxide whose atmospheric levels have risen over time. For example, the partial pressure of CO2 in dry air has risen from about 280 ppm in the 1860s to 385 ppm in 2008. 

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