Sulfuric acid, solutions, heat capacity

Figure 5.1 is a graph of the specific heat capacity cp (heat capacity per gram) of aqueous sulfuric acid solutions at T — 298.15 K against A, the ratio of moles of water to moles of sulfuric acid. The values plotted were obtained from a very... 

Use the heat of solution data in Table B.IO and solution heat capacity data to (a) calculate the enthalpy of a hydrochloric acid, sulfuric acid, or sodium hydroxide solution of a known composition (solute mole fraction) relative to the pure solute and water at 25 C (b) calculate the required rate of heat transfer to or from a process in which an aqueous solution of HCl, H2SO4, or NaOH is formed, diluted, or combined with another solution of the same species and (c) calculate the final temperature if an aqueous solution of HCl, H2SO4, or NaOH is formed, diluted, or combined with another solution of the same species adiabatically. Perform material and energy balance calculations for a process that involves solutions for which enthalpy-concentration charts are available. 

A sulfuric acid solution is labeled 8N (where IN = 1 g-equivalent /L, and 1 mol of H2SO4 contains two g-equivalents). The specific gravity of the solution is 1.230, and its heat capacity is 3.00 J/(g- C). Calculate the specific enthalpy of this solution (in kJ/mol H2SO4) at 60 C relative to pure H2O and an infinitely dilute solution at 25 C. 

Water is added to pure sulfuric acid in a well-insulated flask initially at 25 C and 1 atm to produce a 4.00-molar sulfuric acid solution (SG = 1.231). The final temperature of the product solution is to be 25 C. so that the water added must be chilled liquid T < 25°C), or a mixture of liquid water and ice. Take as a basis of calculation one liter of the product solution and assume Q A// for the process. If you need to know the heat capacity of ice. take it to be half that of liquid water. 

H2S04 aq, r = 49, 40 C) From Table 2.217, p. 2-185 of Perry s Chemical Engineers Handbook (see footnote 1), the heat capacity of a sulfuric acid solution with the given composition is 3.85 J/(g-°C). 

A 2.00 moIe% sulfuric acid solution is neutralized with a 5.00 mole% sodium hydroxide solution in a continuous reactor. All reactants enter at 25 C. The standard heat of solution of sodium sulfate is -1.17 kj/mol Na2S04, and the heat capacities of all solutions may be taken to be that of pure liquid water [4.184 kJ/(kg- C)]. 

The temperature rise of an exothermic reaction is dependent on three factors the heat of the reaction, the heat capacity of the system, and the heat loss of the system The temperature rise of a reaction in a system with no heat loss, the adiabatic temperature rise ( N T), is dependent on the heat of the reaction and the heat capacity of the system, and independent of scale To determine the adiabatic temperature rise of this system, the CDMP/sulfuric acid solution, prewarmed to 30°C, was added all at once to a dewar flask containing the nitric acid/sulfuric acid solution which was also prewarmed to 30°C We observed a temperature rise of 17°C over a period of 4 minutes, with a temperature drop of 1 5°C over the next 4 minutes (Figure 3) We therefore estimated the AT to be about 18.5°C Since this temperature rise was, in theory, independent of scale, we could predict that the large scale nitration reaction would not rise to a temperature of exothermic activity Based on these results, we considered this revised nitration procedure to be safe upon scale up to the pilot plant ... 

The mechanical stability and ion exchange capacity of these condensation resins were modest. A better approach is to prepare a suitable crosslinked base membrane, which can then be converted to a charged form in a subsequent reaction. Ionics is believed to use this type of membrane in many of their systems. In a typical preparation procedure, a 60 40 mixture of styrene and divinyl benzene is cast onto a fabric web, sandwiched between two plates and heated in an oven to form the membrane matrix. The membrane is then sulfonated with 98 % sulfuric acid or a concentrated sulfur trioxide solution. The degree of swelling in the final membrane is controlled by varying the divinyl benzene concentration in the initial mix to control crosslinking density. The degree of sulfonation can also be varied. The chemistry of the process is ... 

One g-mole of pure liquid sulfuric acid at temperature To (°C) is mixed with r g-moles of liquid water, also at temperature 7 o(°C). in an adiabatic container. The final solution temperature is 7,( 0). The mass heat capacities of the pure acid, pure water, and the product solution [J/(g C)j are Cpa, and Cps, respectively, all of which may be taken to be constant (independent of temperature). 

Other heat capacity studies on sulfuric acid and its aqueous solutions are too numerous to mention. However, a recent compilation (9) summarizes much of the work and shows that our adopted heat capacity values for sulfuric acid and its hydrates from room temperature to 80 C are consistent with the available literature. 

Dihydroxybenzaldehyde 5 9 0 A reaction flask (500-ml capacity) is fitted with an efficient stirrer, a reflux condenser, and a wide gas-inlet tube the end of the condenser is connected to, successively, a wash-bottle containing sulfuric acid, an empty safety flask, and a tube that passes over the surface of a sodium hydroxide solution. Resorcinol (20 g) and anhydrous ether (150-200 ml) are placed in the reaction flask, and anhydrous zinc cyanide (1.5 equivalents) is added. Then a rapid stream of dry gaseous hydrogen chloride is passed in. The zinc cyanide disappears as a milky mixture is formed and as the hydrogen chloride dissolves, the imide hydrochloride condensation product separates as a thick oil which solidifies in 10-30 min. The ether is usually saturated in 1.5 h, after which hydrogen chloride is passed in slowly for a further 0.5 h. Then the ether is decanted, water (100 ml) is added to the imide hydrochloride, and the solution is heated to the boiling point, filtered and allowed to cool. About half the aldehyde separates. After this has been collected the remainder of the aldehyde crystallizes in 10-15 h. The total yield is about 95 %, and the m.p. is 135-136° after recrystallization with charcoal from water. 

Variation of pH of Heating Solution. In an attempt to determine the optimum pH of the heating solution, tests were made on films heated in water adjusted to various pH s with sulfuric acid. Within the pH range 1.1 to 10, both the product salt content and the flux were proportional to the pH of the heating solution—the flux characteristics are improved with increasing pH, but at the expense of desalinization capacity of the membrane. 

GRT of particle sizes from 1 to 3 mm was treated by applying thermal, chemical, and combined thermal and chemical treatments to prepare carbonaceous adsorbents for removal of mercury in aqueous solution (Gupta et al., 2011). The adsorbents were prepared by heating the rubber at 400 or 900 C for 2 h in the nitrogen atmosphere and then chemically treating with sulfuric acid, nitric acid, or their mixer solutions for 24 h. The heat treatment of the rubber developed mainly the microporosity, particularly the mesoporosity. The chemical treatment provided the creation of macropores. In the combined heat and chemical treatments, the predominant effects on the porous structure were caused by the treatment that provided the first effect. The adsorption capacity of mercury was larger for the adsorbents of higher microporosity. 

Gardner, W.L. J.W. Cobble, E.C. Jekel, "The thermodynamic properties of high-temperature aqueous solutions. IX. The standard partial molal heat capacities of sodium sulfate and sulfuric acid from 0 to 100"", J. Phys. Chem., v73, 6. p2017 (1969)... 

Preparation of the diluted acid can also be dangerous due to the heat released in the dilution process. The concentrated acid is always added to water and not the other way round, to take advantage of the relatively high heat capacity of water. Addition of water to concentrated sulfuric acid leads to the dispersal of a sulfuric acid aerosol or worse, an explosion. Preparation of solutions greater than 6 M (35%) in concentration is most dangerous, as the heat produced may be sufficient to boil the diluted acid efficient mechanical stirring and external cooling (such as an ice bath) are essential. 

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