One standard atmosphere

The vapour pressure of a liquid increases with rising temperature. A few typical vapour pressure curves are collected in Fig. 7,1, 1. When the vapour pressure becomes equal to the total pressure exerted on the surface of a liquid, the liquid boils, i.e., the liquid is vaporised by bubbles formed within the liquid. When the vapour pressure of the liquid is the same as the external pressure to which the liquid is subjected, the temperature does not, as a rale, rise further. If the supply of heat is increased, the rate at which bubbles are formed is increased and the heat of vaporisation is absorbed. The boiling point of a liquid may be defined as the temperature at which the vapour pressure of the liquid is equal to the external pressure dxerted at any point upon the liquid surface. This external pressure may be exerted by atmospheric air, by other gases, by vapour and air, etc. The boiling point at a pressure of 760 mm. of mercury, or one standard atmosphere, may be termed the normal boiling point. 

Defining fixed points of the International Temperature Scale of 1990 (ITS-90). Except for the triple points, the assigned values of temperature are for equilibrium states at a pressure of one standard atmosphere (101 325 Pa). 

The temperature at which a liquid hoils is not constant, hut varies with the pressure. Thus, while the hoiling point of water is commonly taken as 100°C, this is only true at a pressure of one standard atmosphere (1.013 har) and, hy varying the pressure, the hoiling point can he changed (Table 1.1). This pressure-temperature property can he shown graphically (see Figure 1.2). 

The normal boiling point of a liquid is defined as the temperature at which the vapor pressure of that liquid is exactly one standard atmosphere, 760 mm Hg. 

Bunsen coefficient 13 (dimensionless) Normal Volume of ozone (calculated for STP) dissolved per volume of water at T, when the partial pressure of ozone in the gas phase is one standard atmosphere (= 101 325 Pa) (273.15 K/T) He... 

ICE POINT. The temperature at which, a mixture of air-saturated pure water and pure ice may exist in equilibrium at a pressure of one standard atmosphere,... 

ATMOSPHERE, STANDARD (atm). A unit of pressure. One standard atmosphere equals 101,325 newtons per square meter. 

Solution The barometric pressure is needed to determine vessel pressure from an open-ended manometer. A manometer reading is always a difference between two pressures. See 0005. One standard atmosphere is 760 mm mercury, but on a given day at a given location, the actual ambient pressure may vary. If the barometric pressure on the day of the experiment is 104 kPa, the pressure of the vessel is ... 

The major change from IPTS-68 to ITS-90 has been the elimination of the normal (i.e., 1-atm) boiling points that were previously used as fixed points. This change was made because the temperature of a boiling point is much more sensitive to the ambient pressure than that of a freezing point. The latter is defined as the equilibrium temperature of coexisting pure solid and liquid at one standard atmosphere (101 325 Pa), and corrections can be made for small pressure deviations (the effect is only about 5 mK per atm). ... 

The surface tension of an aqueous solution usually is only slightly influenced by the composition of an adjacent gas phase, but it can be greatly affected by certain solutes. Molecules are relatively far apart in a gas — dry air at 0°C and one standard atmosphere (0.1013 MPa, 1.013 bar, or 760 mmHg) contains 45 mol m-3 compared with 55,500 mol m-3 for liquid water — so the frequency of interactions between molecules in the gas phase and those in the... 

Various units are used for expressing pressures (see Chapter 1, Footnote 8). A pressure of one standard atmosphere, or 0.1013 MPa, can support a column of mercury 760 mm high or a column of water 10.35 m high. As indicated in Chapter 1, the SI unit for pressure is the pascal (Pa), which is 1 N m-2 an SI quantity of convenient size for hydrostatic pressures in plants is often the MPa (1 MPa = 10 bar = 9.87 atm). (An extensive list of conversion factors for pressure units is given in Appendix II, which also includes values for related quantities such as RT.) Pressure is force per unit area and so is dimensionally the same as energy per unit volume (e.g., 1 Pa = 1 N m-2 = 1J m-3). Vw has the units of m3 mol-1, so VWP and hence /aw can be expressed in J mol-1. 

Calculate graphically by plotting logarithm of the vapor pressure versus 1/T-, (e) Vapor pressure at 40 F. Answer 78 psia (b) Boiling point at one standard atmosphere pressure (c) The gage storage pressure required to prevent loss by evaporation at 0 F. 

What is the composition of liquid and vapor of a solution of one mole of w-pentane and 2 moles of n-hexane at 140° P and one standard atmosphere pressure ... 

Historically, the defined pressure for the standard state, i.e., the standard-state pressure, has been one standard atmosphere (101 325 Pa) and most existing data use this pressure. With the growing use of SI units, continued use of the atmosphere is inconvenient. lUPAC has recommended that the thermodynamic data should be reported for a defined standard-state pressure of 100 000 Pa. The standard-state pressure in general is symbolized as Previously in all JANAF thermochemical publications, was taken as 1 atm. In the current set of JANAF Thermochemical Tables p"" is taken as 100 000 Pa (1 bar). It should be understood that the present change in the standard-state pressure carries no implication for standard pressures used in other contexts, e.g., the convention that normal boiling points refer to a pressure of 101 325 Pa (1 atm). 

Pressure is expressed in various units. The SI unit for pressnre is the pascal (Pa), which is 1 kg m s. One standard atmosphere (1 atm) is defined as exactly 1.01325 X 10 Pa. The standard atmosphere is a nsefnl nnit becanse the pascal is inconveniently small and because atmospheric pressure is important as a standard of reference. We must express pressures in pascals when we perform calculations entirely in SI units. 

For historical reasons, a number of different pressure units are commonly used in different fields of science and engineering. Although we will work primarily with the standard atmosphere, it is important that you recognize other units and be able to convert among them. For example, the atmospheric pressure (often called the barometric pressure) recorded in weather reports and forecasts is typically expressed as the height (in millimeters or inches) of the column of mercury it supports. One standard atmosphere supports a 760-mm column of mercury at... 

The weight of the air in each column pushing on the area beneath it exerts a pressure of one standard atmosphere. Each column of air extends to the outer limits of the atmosphere. 

You have learned that atmospheric pressure is measured in mm Hg. Recall from Chapter 10, atmospheric pressure is the force per unit area that the gases in the atmosphere exert on the surface of Earth. Figure 11.5 shows two additional emits that are used to measure pressure of one standard atmosphere. 

The SI emit for measuring pressure is the pascal (Pa), named after the French physicist Blaise Pascal (1623-1662). Because the pascal is a small pressure emit, it is more convenient to use the Idlopascal. As you recall from Chapter 1, the prefix kilo- means 1000 so, 1 Idlopascal (kPa) is equivalent to 1000 pascals. One standard atmosphere is equivalent to 101.3 Idlopascals. 

If the unit of area is the square inch and the unit of force is the pound, then the unit of pressure is the pound per square inch (psi). Expressed in these units, one standard atmosphere is 14.7 pounds per square inch or 14.7 psi. ... 

Expressed in SI units, one standard atmosphere is 101 300 pascals. Note that SI units are based on the square meter area and not the square inch. ... 

You can use Table 11.1 to convert pressure measurements to other imits. For example, you can now find the absolute pressure of the air in a bicycle tire. Suppose the gauge pressure is 44 psi. To find the absolute pressure, add the atmospheric pressure to the gauge pressure. Because the gauge pressure is given in pounds per square inch, use the value of the standard atmosphere that is expressed in pounds per square inch. One standard atmosphere equals 14.7 psi. 

In weather reports, barometric pressure is often expressed in inches of mercury. What is one standard atmosphere expressed in inches of mercury ... 

You know that one standard atmosphere is equivalent to 760 mm of Hg. What is that height expressed in inches A length of 1.00 inch measures 25.4 mm on a meterstick. 

At sea level, the pressure exerted by gases of the atmosphere equals one standard atmosphere (1 atm). 

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