Pressure of Liquids

Consider the most common case of boiling. At equilibrium Guq = Gyap so t/Guq = t(Gyap. For the boiling process the most appropriate variables to use are P, T with the assumption that there is some equation of state that will relate P, V, T, and n. Thus, we can relate the general differential of G to one of the HUG A equations. 

The Clapeyron equation was extended to a more usable form by a German physicist R. G. 

Clausius (1822-1888) by splitting the — differential and integrating the new form using the ideal 

Graphically, this leads to a plot similar to the case of the temperature dependent equilibrium constant shown above in the section on equUibrimn. We see that we can plot a logarithm of the pressure against reciprocal Kelvin temperature and expect to find a straight line with a negative slope. 

This can be integrated as the final working equation becomes the very useful Clausius-Clapeyron equafion 

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An elementary account of the subject has been given in the previous Section. For the fractional distillation under diminished pressure of liquids diflfering only slightly in boiling point, a firactionating column (see Sections 11,15 and 11,17) must be used. Provision must, of course, be made for the insertion of a capillary tube into the fiask containing the mixture. This can be done by any of the following methods —... 

Fig. 33. Vapor pressure of liquid chlorine as a function of temperature (78).

TABLE 2-4 Vapor Pressure of Liquid Water from -16 to 0"C ... 

P = pressure of liquid Vl = volume of hquid Ey = Young s modulus of elasticity V = Poisson s ratio... 

H is placed at the highest available level (Note 5) and connected with the tubes 7, 7, and K in such a manner as to secure a pressure of liquid sufficient to more than balance the steam pressure (Note 6). E and F are specially constructed condensers of unusual length (160 cm. and 85 cm., respectively) and bore (40 mm.) made from large glass tubing and rubber stoppers (Note 7). I he top of condenser E is connected to a good draft chamber. 

Ion-exchange chromatography involves an electrostatic process which depends on the relative affinities of various types of ions for an immobilised assembly of ions of opposite charge. The stationary phase is an aqueous buffer with a fixed pH or an aqueous mixture of buffers in which the pH is continuously increased or decreased as the separation may require. This form of liquid chromatography can also be performed at high inlet pressures of liquid with increased column performances. 

P,. = Vapor pressure of liquid at body inlet temperature, psia... 

Storage Vessels Vapor pressure of liquid at maximum ambient temperature plus 30° F. (usually 110° to 140° F.)... 

APPROX. VAPOR PRESSURE OF LIQUID-EXHAUST STEAM-------------------... 

Pj, = Brake horsepower at shutoff or no flow P[d = Differential pressure between absolute pressures at outlet and inlet to pump, psi P,p = Vapor pressure of liquid at pumping temperature, psia... 

Fluid power encompasses most applications that use liquids or gases to transmit power in the form of mechanical work, pressure and/or volume in a system. This definition includes all systems that rely on pumps or compressors to transmit specific volumes and pressures of liquids or gases within a closed system. The complexity of these systems range from a simple centrifugal pump used to remove casual water from a basement to complex airplane control systems that rely on high-pressure hydraulic systems. 

In this case, Ptot is the measured pressure. The partial pressure of water vapor, Ph2o, is equal to the vapor pressure of liquid water. It has a fixed value at a given temperature (see Appendix 1). The partial pressure of hydrogen, PH2, can be calculated by subtraction. The number of moles of hydrogen in the wet gas, h2, can then be determined using the ideal gas law. 

If the total pressure of the vapour at constant temperature is represented as a function of the compositions of the two phases, the p-liquid and p-vapour curves are obtained. The p-liquid curves—that is, the curves representing the total vapour pressures of liquid binary mixtures as functions of the composition of the liquid phase—are most important they are usually referred to simply as the vapour-pressure curves of the mixture. Each curve is an isotherm. 

Another expression that does a reasonably good job of representing vapor pressures of liquids, if the temperature range is not too great, is the Antoine equation ... 

E8.5 The vapor pressure of liquid helium can be expressed by the equation... 

Calculate the standard entropy of vaporization of water at 85°C, given that its standard entropy of vaporization at 100.°C is 109.0 J-K -mol 1 and the molar heat capacities at constant pressure of liquid water and water vapor are 75.3 J-K -mol 1 and 33.6 J-K -mol, respectively, in this range. 

Br(g) from the thermodynamic data provided in Appendix 2A. (b) What is the vapor pressure of liquid bromine (c) What is the partial pressure of Br(g) above the liquid in a bottle of bromine at 25°C (d) A student wishes to add 0.0100 mol Br2 to a reaction and will do so by filling an evacuated flask with Br2 vapor from a reservoir that contains only bromine liquid in equilibrium with its vapor. The flask will be sealed and then transferred to the reaction vessel. What volume container should the student use to deliver 0.010 mol Br2(g) at 25°C ... 

Liquid carbon dioxide is usually stored under 20 bar pressure at — 18°C. Compression and cooling of the gas between the temperature limits at the triple point and the critical point will cause it to liquefy. The triple point is the pressure temperature combination at which carbon dioxide can exist simultaneously as gas, liquid and solid. Above the critical temperature point of 31°C it is impossible to liquefy the gas by increasing the pressure above the critical pressure of 73 bar. Reduction in the temperature and pressure of liquid below the triple point causes the liquid to disappear, leaving only gas and solid. (Solid carbon dioxide is also available for cryogenic work and at —78°C the solid sublimes at atmospheric pressure.)... 

A fundamental property of a substance is the tendency for its atoms or molecules to spread into the surrounding space. A consequence of this property is the observed vapor pressure of liquids and solids. In order to understand the effects of the formation of a solution on this property, reference may be drawn to a solution consisting of two substances, A and B, with A being the solvent and B the solute. If the vapor pressure, PA, of the solvent over the solution is considered, it is clear that it must be proportional to the amount of A present in the solution. Thus,... 

Temperature and operating pressure of liquid ammonia-gas separator, 340 bar and -28 °C. 

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