Sulfuric acid enthalpy

The calculation of the enthalpies of formation of organic sulfur compounds from the experimental results for their energies of combustion, requires an accurate knowledge of the enthalpy of formation of aqueous sulfuric acid. Enthalpies of formation of [H2SO4 n H2O] where n = 1 to 00 are available from the NBS Tables of Chemical Thermodynamic Properties [41]. The value usually taken for n in combustion calorimetry is n = 115 being Af//°([H2S04 115 H2OKI)) = -(887.811 0.042) kJmor. ... 

A tabulation of the partial pressures of sulfuric acid, water, and sulfur trioxide for sulfuric acid solutions can be found in Reference 80 from data reported in Reference 81. Figure 13 is a plot of total vapor pressure for 0—100% H2SO4 vs temperature. References 81 and 82 present thermodynamic modeling studies for vapor-phase chemical equilibrium and liquid-phase enthalpy concentration behavior for the sulfuric acid—water system. Vapor pressure, enthalpy, and dew poiat data are iacluded. An excellent study of vapor—liquid equilibrium data are available (79). 

Enthalpy-Concentration Diagram for Aqueous Sulfuric Acid... 

FIG. 2-30 Entbalpy-concentration diagram for aqueous sulfuric acid at 1 atm. Reference states enthalpies of pure-bquid components at 32 F and vapor pressures are zero. NOTE It should be observed that the weight basis includes the vapor, which is particularly important in the two-phase region. The upper ends of the tie bnes in this region are assumed to be pure water. (Hougen and Watson, Chemical Process Principles, I, Wiley, New York, 1943. )... 

Enthalpy of Nitric Acid, Sulfuric Acid, and Water Mixtures.. 

Enthalpy of nitric acid, sulfuric acid, and water mixtures McKinley and Brown (Ref 28a)... 

Relative partial molar enthalpies can be used to calculate AH for various processes involving the mixing of solute, solvent, and solution. For example, Table 7.2 gives values for L and L2 for aqueous sulfuric acid solutions7 as a function of molality at 298.15 K. Also tabulated is A, the ratio of moles H2O to moles H2S(V We note from the table that L — L2 — 0 in the infinitely dilute solution. Thus, a Raoult s law standard state has been chosen for H20 and a Henry s law standard state is used for H2SO4. The value L2 = 95,281 Tmol-1 is the extrapolated relative partial molar enthalpy of pure H2SO4. It is the value for 77f- 77°. 

However, the fact that the derived S—O bond dissociation energy in sulfuric acid is identical to that found in the acid derivatives, strongly supports the estimated enthalpy of formation for gas-phase sulfurous acid given by Benson18. 

Two successive stages in the industrial manufacture of sulfuric acid are the combustion of sulfur and the oxidation of sulfur dioxide to sulfur trioxide. From the standard reaction enthalpies... 

The freezing point depression of a solvent is proportional to the concentration of solute particles and may be used to measure the extent of ionization once the new particles have been identified qualitatively as ions. The method has the obvious disadvantage of not allowing measurements over a range of temperatures in a single solvent. It is almost certainly not worth while to compute an enthalpy of ionization from ionization constants at two different temperatures in two different solvents. Usable solvents are limited not only by the requirement that the melting point be at a convenient temperature but also by the requirement that the solvent be capable of producing ions yet not be sufficiently nucleophilic to react irreversibly with them once they are formed. For this reason most cryoscopic work has been done in sulfuric acid or methanesulfonic acid.170... 

O Concentrated sulfuric acid can be diluted by adding it to water. The reaction is extremely exothermic. In this question, you will design an experiment to measure the enthalpy change (in kj/mol) for the dilution of concentrated sulfuric acid. Assume that you have access to any equipment in your school s chemistry laboratory. Do not carry out this experiment. 

Liquid sulfuric acid has a very large negative standard enthalpy of formation (-814.0 kJ/mol). Write an equation to show the formation of liquid sulfuric acid. The standard state of sulfur is rhombic sulfur (S(s)). 

When a solute is dissolved in a solvent, heat may either be evolved (as with sulfuric acid in water, where strong heating is observed) or absorbed (as with ammonium nitrate in water, where strong cooling is observed). Thus the dissolution may be either exothermic or endothermic, and the standard molar enthalpy of solution, is then either negative or positive. The sign of AsaJl°... 

Table 8 Enthalpies of Extraction of Uranyl from Sulfuric Acid by Organoamines82 83,83...

Polymer catalysts showing interactions with the substrate, similar to enzymes, were prepared and their catalytic activities on hydrolysis of polysaccharides were investigated. Kinetical analyses showed that hydrogen bonding and electrostatic interactions played important roles for enhancement of the reactions and that the hydrolysis rates of polysaccharides followed the Michaelis-Menten type kinetics, whereas the hydrolysis of low-molecular-weight analogs proceeded according to second-order kinetics. From thermodynamic analyses, the process of the complex formation in the reaction was characterized by remarkable decreases in enthalpy and entropy. The maximum rate enhancement obtained in the present experiment was fivefold on the basis of the reaction in the presence of sulfuric acid. 

The activation enthalpy of the overall reaction in the presence of the copolymer is smaller than that in the presence of sulfuric acid. However, the activation entropy is also smaller. As the result, activation free energy of the overall reaction in the presence of the copolymer is only slightly smaller than that in the presence of sulfuric acid. 

In perchloric acid, hexoses and pentoses are oxidized by Ce(IV) via formation of two complex intermediates. The first is partly oxidized following Michaelis-Menten kinetics and partly dissociated to the second, which is oxidized more slowly than the former.180 The first step in the oxidation of aldoses by Tl(III) in the same medium involves the C-l-C-2 cleavage of the aldehydo form of the sugar. Thus, D-glucose gives D-arabinose and formic acid. With an excess of oxidant the final product is carbon dioxide.181 In the presence of a catalytic amount of sulfuric acid in acetic acid, Tl(III) oxidizes maltose and lactose to the corresponding disaccharide aldonic acids. The reaction showed activation enthalpies and enthropies characteristic of second-order reactions.182... 

The mixing process is carried out in two steps First, the pure sulfuric acid and the. solution are mixed, and the total heat of part (a) is extracted second, the pure water is adiabatically. What is the enthalpy of the intermediate solution formed in the first step ... 

Enthalpy/concentration diagram, 440-447 for sodium hydroxide/water, 444 for sulfuric acid/water, 441 Enthalpy/entropy (Mollier diagram), 183, 185 for steam (see back endpapers)... 

Mixing of H2S04(f) and H20(f) releases heat. This means that the enthalpy of sulfuric acid is lower than the combined enthalpies of its components. 

TABLE 21.6 Enthalpies, entropies, and Gibbs free energy of hydration for sulfuric acid dimer calculated at T = 298.15 K and P = 101.3 kPa. Abbrevi- ... 

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