Vaporization of water

Eigure 3 is a flow diagram which gives an example of the commercial practice of the Dynamit Nobel process (73). -Xylene, air, and catalyst are fed continuously to the oxidation reactor where they are joined with recycle methyl -toluate. Typically, the catalyst is a cobalt salt, but cobalt and manganese are also used in combination. Titanium or other expensive metallurgy is not required because bromine and acetic acid are not used. The oxidation reactor is maintained at 140—180°C and 500—800 kPa (5—8 atm). The heat of reaction is removed by vaporization of water and excess -xylene these are condensed, water is separated, and -xylene is returned continuously (72,74). Cooling coils can also be used (70). 

It should be noted that the highest possible absorption rates will occur under conditions in which the hquid-phase resistance is negligible and the equilibrium back pressure of the gas over the solvent is zero. Such situations would exist, for instance, for NH3 absorption into an acid solution, for SO9 absorption into an alkali solution, for vaporization of water into air, and for H9S absorption from a dilute-gas stream into a strong alkali solution, provided there is a large excess of reagent in solution to consume all the dissolved gas. This is known as the gas-phase mass-transfer limited condition, wrien both the hquid-phase resistance and the back pressure of the gas equal zero. Even when the reaction is sufficiently reversible to allow a small back pres-... 

Whenever these conditions on the ratio yjy apply, the design can be based upon the physical rate coefficient /cg or upon the height of one gas-phase mass-transfer unit He- The gas-phase mass-transtor hmited condition is approximately vahd, for instance, in the following systems absorption oi NH3 into water or acidic solutions, vaporization of water into air, absorption of H9O into concentrated sulfuric acid solutions, absorption of SO9 into alkali solutions, absorption of H9S from a dllute-... 

Steam explosion rapid vaporization of water within molten metal, molten salts or hot oil or through them eontaeting surfaee or adsorbed moisture (refer to page 47). 

Cp = Speeific heat of the desuperheating water, Btu/lb-°F h, = Enthalpy of superheated system, Btu/lb hj = Enthalpy of saturated steam, Btu/lb Lh = latent heat of vaporization of water at t,j Btu/lb m = Mass of superheated steam into the system, Ib/hr mj = Mass of saturated steam out, Ib/hr n = Mass of desuperheating water used, Ib/hr t[ = Temperature of superheated steam, °F = Temperature of saturated steam, °F t,j, = Temperature of desuperheating water, °F... 

FIGURE 4.38 (a) The uniform vaporization of water in paper, (b) Resistance web analogy for... 

The latent heat of vaporization for hydrocarbon compounds is given in Table 2-9. The latent heat of vaporization of water is given by hfj, in the steam table (Table 2-6). 

Other incidents caused by the sudden vaporization of water are described in Sections 12.2 and 12.4.5. 

The hazards of water hammer are described in Section 9,1,5 and the hazards of ice formation in Section 9,1,1, This section describes some accidents that have occurred as the result of the sudden vaporization of water, incidents known as boilovers, slopovers, foamovers, frothovers, or puking, Boilover is used if the tank is on fire and hot residues from the burning travel down to the water layer, Slopover is often used if water from fire hoses vaporizes as it enters a burning tank. Sections 9,1.1 and 12.4.5 describe incidents in which vessels burst because water that had... 

From a slightly different point of view, we can say that the equation T = AH°/AS° allows us to calculate the temperature at which a chemical or physical change is at equilibrium at 1 atm pressure. Consider, for example, the vaporization of water. 

Plasma No Ceramic- Vapors of water and Special equipment is... 

Suppose we wish to evaporate one mole of water, as expressed in equation (7). One mole contains the Avogadro number of molecules (6.02 X 1023) and has a weight of 18.0 grams. Using a calorimeter, as you did in Experiment 5, you could measure the quantity of heat required to evaporate one mole of water. It is 10 kilocalories per mole. This value is called the molar heat of vaporization of water. This is the energy required to separate 6.02 X 1023 molecules of water from one another, as pictured in Figure 5-1. 

The heat accompanying the phase change (2) is 1.44 kcal/mole. This is much less than the molar heat of vaporization of water, 10 kcal/mole. Table 5-II contrasts the melting points and the heats of melting per mole (the molar heat of melting, or the molar heat of fusion) of the same pure substances listed in Table 5-1. 

How much heat is evolved if one pound (454 grams) of lime is slaked according to reaction (70) How many grams of water can be evaporated with this heat (The heat of vaporization of water is about 10 kcal/mole.)... 

E6.2 The fugacity of liquid water at 298.15 K is approximately 3,17 kPa. Take the ideal enthalpy of vaporization of water as 43.720 TmoD1, and calculate the fugacity of liquid water at 300 K. 

In hot, dry climates an inexpensive alternative to air conditioning is the swamp cooler. In this device water continuously wets porous pads through which fans blow the hot air. The air is cooled as the water evaporates. Use the information in Tables 6.2 and 6.3 to determine how much water must be evaporated to cool the air in a room of dimensions 4.0 m X 5.0 m X 3.0 m by 20.°C. Assume that the enthalpy of vaporization of water is the same as it is at 25°C. 

Self-Test 7.6B Calculate the standard entropy of vaporization of water at its boiling point (see Table 6.3). 

Self-Test 7.14A Calculate the entropy change of the surroundings when 1.00 mol H20(l) vaporizes at 90°C and I bar. Take the enthalpy of vaporization of water as 40.7 kj-mol. ... 

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. 

As we saw in Section 5.1, a single substance can exist in different phases, or physical forms. The phases of a substance include its solid, liquid, and gaseous forms and its different solid forms, such as the diamond and graphite phases of carbon. In one case—helium—two liquid phases are known to exist. The conversion of a substance from one phase into another, such as the melting of ice, the vaporization of water, and the conversion of graphite into diamond, is called a phase transition (recall Section 6.11). 

C14-0133. The enthalpy of sublimation of Ice at 273.15 K Is not the simple sum of the enthalpies of fusion and vaporization of water, but it can be calculated using Hess law and an appropriate path that Includes fusion and vaporization. Devise such a path, show it on a phase diagram for water, and carry out the calculation, making reasonable assumptions If necessary (C(liquid water) = 75.3 7 mol K , and C(water vapor) = 33.6 K ). 

The slope of the line allows for the determination of the enthalpy of vaporization of water, A//Vap, and the y intercept yields the entropy of vaporization, A. S vap As both the enthalpy and the entropy of water increase as the phase change liquid — vapor occurs, the slope and y intercept of the Clausius-Clapeyron equation are negative and positive, respectively. At 373 K these thermodynamic quantities have values of AHvap = 40.657 kJ mol-1 and ASvap = 109.0 J K-1 mol-1. The leavening action due to water vapor or steam arises from the increased amount of water vapor that forms as pastry temperatures initially rise in the oven and then from the increased volume of the water vapor as temperatures continue... 

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