Normal atmospheric equilibrium

Because Pj = 1 atm, these concentrations are called normal atmospheric equilibrium concentrations, or NAEC. NAECs for the most common gases in seawater (35%o) over the range of temperatures encountered in the surfece ocean are shown in Table 6.2. 

NAEC, normal atmospheric equilibrium concentration The gas concentration that a water mass would attain if it reached equilibrium with the atmosphere. The NAEC of a gas is a function of water temperature and salinity as well as the partial pressure of the gas in the atmosphere. 

Normal atmospheric equilibrium concentrations (NAEC) concentrations based on expected equilibrium conditions, between water and atmosphere, at a particular pressure, temperature, salinity, and humidity. 

This chart is applicable only to flammable liquids or gases in equilibrium In a closed container. Mixtures of vapor and air will be too lean to burn at temperatures below and at pressures above the values shown by the line on the chart for any substance. Conditions represented by points to the left of and above the respective lines are accordingly nonflammable. Points where the diagonal lines cross the zero gauge pressure line (760 mm of mercury absolute pressure) indicate flash point temperatures at normal atmospheric pressure. 

Table 21.21 Oxygen dissolved in sea-water in equilibrium with a normal atmosphere (101 325 N m" ) of air saturated with water vapour ...

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). 

The conditions that apply for the saturated liquid-vapor states can be illustrated with a typical p-v, or (1 /p), diagram for the liquid-vapor phase of a pure substance, as shown in Figure 6.5. The saturated liquid states and vapor states are given by the locus of the f and g curves respectively, with the critical point at the peak. A line of constant temperature T is sketched, and shows that the saturation temperature is a function of pressure only, Tsm (p) or psat(T). In the vapor regime, at near normal atmospheric pressures the perfect gas laws can be used as an acceptable approximation, pv = (R/M)T, where R/M is the specific gas constant for the gas of molecular weight M. Furthermore, for a mixture of perfect gases in equilibrium with the liquid fuel, the following holds for the partial pressure of the fuel vapor in the mixture ... 

Equilibrium moisture content curves vary greatly with the type of material examined. Insoluble, non-porous materials, such as talc or zinc oxide, have equilibrium moisture contents of almost zero over a wide humidity range. A moisture content between 10 and 15% may be expected for cotton fabrics under normal atmospheric conditions. Drying below the equilibrium moisture content for room conditions may be deliberately undertaken, particularly if the material is unstable in the presence of moisture subsequent storage becomes important. 

Investigations of the state of carbonate equilibrium of water which is transiting the vadose zone have not been numerous. The equilibrium COj (carbon dioxide partial pressure) and state of saturation with respect to calcite was studied by Holland et al. (1964) in Indian Echo Cave, Pennsylvania, and Luray Caverns, Virginia, and by Thrailkill (1971) in Carlsbad Caverns, New Mexico. These investigations showed that seepage water entering the cave was in equilibrium with a f cO2 much higher than that of the normal atmosphere and was often supersaturated with respect to calcite. 

Boiling point is the temperature at which the liquid and gas phases of a pure substance are in equilibrium at a specified pressure, that is, the temperature at which the substance changes its state from a liquid to a gas at a given pressure. The normal boiling point is the boiling point at normal atmospheric pressure (101.325 kPa). The SI units are Kelvin degrees K, nevertheless the Celsius degrees °C are still very much in use (°C = K — 273.15). 

Ammonia decomposition, on the other hand, may be carried out under more favorable conditions. Stoichiometry favors low pressure, 0 normal atmospheric-pressure equipment is sufficient. Equilibrium yields increase with temperalun and kinetic rates are measured with precision. This is why ammonia decomposition, which is less interesting, has historically received so much attention in the search for improved synthesis catalysts. ... 

Figure 4. Noble gas components in a shallow ground-water sample. All concentrations are normalized to the respective atmospheric equilibrium concentration (given as 100 %). Note that the excess air component for Xe and the radiogenic component for He are too small to be clearly visible on this scale. The data represent an actual sample from southern France, which was interpreted assuming unfractionated excess air. It has an infiltration temperature of 10.8°C, an excess air...

Boiling point - The temperature at which the liquid and gas phases of a substance are in equilibrium at a specified pressure. The normal boiling point is the boiling point at normal atmospheric pressure (101.325 kPa). 

First, let us examine homogeneous (no precipitates), open systems. In these systems the carbonate species in solution are in equilibrium with the CO2 gas in the atmosphere above the solution. The normal atmosphere contains 10 - atm of CO2, and when this is in equilibrium with C02(a<,) from Eqs. 4-103 and 4-110, we obtain... 

Let us asume that the stabilization pond effluent is in equilibrium with the normal atmosphere that contains 21 percent oxygen. Knowing that the pH is 7,8, we find that... 

For example, in dry climates (low humidity), snow and ice seem to sublime— a minimum amount of slush is produced. Wet clothes put on an outside line at temperatures below 0°C freeze and then dry while frozen. However, the phase diagram (Fig. 16.55) shows that ice should not be able to sublime at normal atmospheric pressures. What is happening in these cases Ice in the natural environment is not in a closed system. The pressure is provided by the atmosphere rather than by a solid piston. This means that the vapor produced over the ice can escape from the immediate region as soon as it is formed. The vapor does not come to equiHbrium with the solid, and the ice slowly disappears. Sublimation, which seems forbidden by the phase diagram, does seem to occur under these conditions, but it is not sublimation under equilibrium conditions. 

Accordingly, when water is in equilibrium with air in nature, H3O and HC03 will contribute to additional DC conductivity and a reduction of pH. The reduction in pH is actually substantial—the pH of pure (nonpolluted) water lowers to 5.7 (acid) when in equilibrium with normal atmospheric CO2 concentration levels (0.03%). 

Talc loses its water of hydration at 1000°C. At this temperature, the talc crystal restructures itself to form the mineral enstatite (MgSiOs), which is significantly harder than talc, with a Mohs hardness of 5-6, and less platy. Talc is inert to most chemicals. It normally will absorb an equilibrium 0.2-0.3% by weight of moisture under normal atmospheric conditions. 

Boiling point is defined as the temperature at which a liquid and the vapor (gas) above it are in equilibrium. At normal atmospheric pressure, the boiling point of a liquid will be the temperature at which the liquid is at equilibrium with the atmosphere above the liquid (atmospheric pressure). Another way to say this is that boiling point is the temperature at which molecules leave the liquid phase and are moved into the gas phase. Several factors are important in determining the boiling point of a liquid. The number of atoms in a molecule and the number and type of heteroatom functional groups will play an important role. 

Stable phase equilibria are the thermodynamic equilibria. In order to reach the isothermal dissolve equilibrium, the apparatus mainly contains two parts i.e. constant temperature installing and equilibrator. Therefore, experimental apparatus depends on the target of temperature. Generally, thermostatic water-circulator bath is used under normal atmospheric temperature, and thermostatic oil-circulator bath is chosen at higher level... 

Here, Cp is isobaric specific heat of gaseous (approximated by a constant), and is heat of evaporation of H2O at (Tq,Pq). [To be precise, if for example Tq = 273 K and Pq is normal atmospheric pressure then the value of is, in fact, extrapolated because liquid water is not in equilibrium with its vapour at these conditions such extrapolated values are quite common in thermodynamic tables.]... 

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