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1.
The Planck‐Benzinger methodology provides a means of determining the innate temperature‐invariant enthalpy, Δ H°( T0), thermal agitation energy, or the heat capacity integrals ∫Δ Cp°( T) dT, and allows precise determination of 〈 TCp〉, 〈 Th〉, 〈 Ts〉, and 〈 Tm〉. It is a method for evaluating [Δ H ? Δ H°( T0)], the heat of reaction for biologic molecules at room temperature, and provides for a better understanding of cooperative thermodynamic compensation. The Planck‐Benzinger methodology demonstrates that macromolecular interactions will always exhibit a negative value of the Gibbs free energy change at a well‐defined temperature. It can be used for determination of the thermodynamic molecular switch, where there is a change of sign in Δ Cp°( T) reaction which determines the behavior patterns of the Gibbs free energy change. All interacting biologic systems that we have thus far examined using the Planck‐Benzinger approach point to the universality of this thermodynamic switch. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
2.
For the first time, the heat capacity $ C_{\text{p}}^{^\circ } $ of poly(2-ethylhexyl acrylate) has been studied in an adiabatic vacuum calorimeter between 7 and 350 K, the standard thermodynamic functions: heat capacity $ C_{\text{p}}^{^\circ } $ ( T), enthalpy H°( T) ? H°(0), entropy S°( T) ? S°(0), Gibbs function G°( T) ? H°(0) have been calculated from T → 0 to 350 K. The energy of combustion Δ c U of the compound under study has been measured in a calorimeter with a stationary bomb and an isothermal shell. The standard enthalpy of combustion Δ c H° and thermodynamic parameters of formation—enthalpy Δ f H°, entropy Δ f S°, Gibbs function Δ f G°—at T = 298.15 K have been calculated. The results have been used to calculate the thermodynamic characteristics of 2-ethylhexyl acrylate bulk polymerization into poly(2-ethylhexyl acrylate) over the range from T → 0 to 350 K. 相似文献
3.
For a set of 32 selected free radicals, energy minimum structures, harmonic vibrational wave numbers ω e, principal moments of inertia IA, IB, and IC, heat capacities C° p( T), entropies S°( T), thermal energy contents H°( T) ? H°(0), and standard enthalpies of formation Δ fH°( T) were calculated at the G3MP2B3 level of theory in the temperature range 200–3000 K. In this article, thermodynamic functions at T = 298.15 K are presented and compared with recent experimental values. The mean absolute deviation between calculated and experimental Δ fH°(298.15) values resulted in 3.91 kJ mol ?1, which is close to the average experimental uncertainty of ± 3.55 kJ mol ?1. The influence of hindered rotation on thermodynamic functions is studied for isopropyl and tert‐butyl radicals. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 550–560, 2002 相似文献
4.
The thermodynamic properties and oxygen stoichiometry of Ba 2Cu 3O 5 + δ are studied by means of the electromotive force (EMF) with a fluoride electrolyte, dissolution calorimetry, and thermogravimetry. It is shown that the temperature dependence of the Gibbs energy of the formation of barium cuprate from simple oxides and oxygen in the temperature range of 860–1120 K can be described by the polynomial Δ f, ox G °(Ba 2Cu 3O 5 + δ) ± 0.1 (kJ/mol) = ?291.78 + 1.127 T ? 0.13207 Tln T (kJ/mol). 相似文献
5.
The rubber elastic behaviors of long polymethylene (PM) chains are investigated using Monte Carlo simulations and considering the rotational‐isomeric‐state model. Through the Monte Carlo method we can generate many PM chains in the equilibrium states, and obtain the average Helmholtz free energy 〈 A〉 and average energy 〈 U〉. Chain dimensions and thermodynamic statistical properties of long PM chains under various elongation ratios λ are also calculated. We find that the elastic force f increases with elongation ratio λ, and that energy contribution fu to the elastic force is negative and significant. The ratio fu / f ranges from –0.37 to –0.32 at T = 300 K and from –0.53 to –0.40 at T = 413 K, and decreases with increasing temperature, which agrees with the experimental data. Our calculations may provide some insights into the macroscopic phenomena of rubber elasticity. 相似文献
6.
The aggregation behavior of metal dodecyl sulfates (MDS), [Na 1+, Mg 2+, Mn 2+, Co 2+, and Ni 2+] in water has been studied by electrical conductivity (at 293.15–333.15 K) and surface tension methods (at 303.15 K). Critical micelle concentrations (CMCs), degree of counterion dissociation (β) evaluated from conductivity data. Using law of mass action model, the thermodynamic parameters viz. Gibbs energy (ΔG m 0), enthalpy (ΔH m 0), and entropy (ΔS m 0) were evaluated. The enthalpy of micellization decreases strongly with increasing temperature. ΔG is always negative (thermodynamically favored process) and slightly temperature and counterion dependent. Gibbs energy and entropy exploit micellization as thermodynamic favorable process. The electrostatic repulsions between ionic head groups, which prevent the aggregation, are progressively screened as the ionic character decreases with the size of the counterion. The plots of differential conductivity, (dk/dc) T,P , versus the total surfactant concentration enables us to determine the CMC values more precisely than the conventional method. Surfactants with strong condense counterion are adapted to rodlike micelle better than to a spherical micelle. The data are explained in terms of molecular characteristics of surfactants viz. degree of dissociation, polar head group size and counterion. 相似文献
7.
α,β‐Unsaturated amino acids (dehydroamino acids) have been found in naturally occurring antibiotics of microbial origin and in some proteins. Due to the presence of the C αC β double bond, the dehydroamino acids influence the main‐chain and the side‐chain conformations. The lowest‐energy conformational state of the model tripeptides, Ac–X–ΔAla–NHMe, (X=Ala, Val, Leu, Abu, or Phe) corresponds to ϕ 1=−30°, ψ 1=120° and ϕ 2=ψ 2=30°. This structure is stabilized by the hydrogen bond between CO of the acetyl group and the NH of the amide group, resulting in the formation of a 10‐membered ring. In the model heptapeptide containing ΔAla at alternate position with Ala, Abu, and Leu, the lowest‐energy conformation corresponds to ϕ=−30° and ψ=120° for all the Ala, Abu, and Leu residues and ϕ=ψ=30° for all ΔAla residues. A graphical view of the molecule in this conformation reveals the formation of three hydrogen bonds involving the CO moiety of the ith residue and the NH moiety of the i+3th residue, resulting in a 10‐membered ring formation. In this structure, only alternate peptide bonds are involved in the intramolecular hydrogen‐bond formation unlike the helices and it has been named the β‐bend ribbon structure. The helical structures were predicted to be the most stable structures in the heptapeptide Ac–(Aib–ΔAla) 3–NHMe with ϕ=±30°, ψ=±60° for Aib residues and ϕ=ψ=±30° for ΔAla residues. The computational results reveal that the ΔAla residue does not induce an inverse γ‐turn in the preceding residue. It is the competitive interaction of small solvent molecules with the hydrogen‐bonding sites of the peptide which gives rise to the formation of an inverse γ‐turn (ϕ 1=−54°, ψ 1=82°; ϕ 2=44°, ψ 2=3°) in the preceding residue to ΔAla. The computational studies for the positional preference of ΔAla in the peptide containing one ΔAla and nine Ala residues reveals the formation of a 3 10 helical structure in all the cases with the terminal preferences for ΔAla, consistent with the position of ΔAla in the natural antibiotics. The extended structures is found to be the most stable for poly‐ΔAla. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 15–23, 1999 相似文献
8.
In the present research, the temperature dependence of heat capacity of tris(pentafluorophenyl)-4-pyridylethylgermane (C6F5)3Ge–CH2–CH2–C5H4N was studied by precise adiabatic vacuum calorimetry and differential scanning calorimetry over the temperature range from 6 to 450 K. The temperature and enthalpy of fusion of tris(pentafluorophenyl)-4-pyridylethylgermane and the total mole fraction of impurities have been determined. The thermal stability of the sample was investigated by thermogravimetric analysis. The experimental data were used to calculate the standard thermodynamic functions: heat capacity, enthalpy, entropy, and the Gibbs energy over the range from T → 0 to 420 K for crystalline and liquid states. For the compound under study, the standard entropy of formation in the crystalline state was calculated at T = 298.15 K. In addition, the structure of the investigated compound was established, and corresponding structural parameters were determined. 相似文献
9.
The thermodynamic properties of a series of polystyrene samples with different molecular weights ( M w was varied from 2.5·10 3 to 6.57·10 4) were studied by precision adiabatic vacuum, high-accuracy dynamic, and combustion calorimetry: temperature dependences of the heat capacity in a wide temperature range, thermodynamic characteristics of glass transition and glassy state under standard pressure, and energy of combustion. The thermodynamic functions C ○ p ( T), H ○( T) - H ○(0), S ○( T) - S ○(0), and G ○( T) - H ○(0) of polystyrene with different molecular weights, enthalpies of combustion Δ c H ○, thermodynamic parameters of formation from simple substances Δ f H ○, Δ f S ○, and Δ f G ○ at T = 298.15 K, and parameters of their synthesis from monomers were calculated from the experimental data. The temperature dependences of the heat capacity for a region of 0–380 K, glass transition temperatures, and thermodynamic characteristics of formation and synthesis of polystyrene depending on its molecular weight were examined. 相似文献
10.
Heat capacity at constant pressure C
p
( T) of a dysprosium boride DyB 62 single crystal obtained by zone melting was studied experimentally in the temperature range of 2 to 300 K. Abnormally high
values of dysprosium boride heat capacity were revealed in the range of 2–20 K, due to the magnetic contribution and the effect
of disorder in the boride lattice. Temperature changes in DyB 62 enthalpy, entropy, Gibbs energy, and standard values of these thermodynamic functions were calculated. 相似文献
11.
By high-precision dynamic calorimetry the temperature dependences of heat capacity of dimethylene urethane (DMU) between 320 and 370 K and partially crystalline poly(dimethylene urethane) (PDMU) in the range 326-490 K at standard pressure have been determined within ±1.5%. The thermodynamic characteristics of fusion of the substances, namely the temperature interval of melting, temperature, enthalpy and entropy of fusion, as well as the characteristics of devitrification and glassy state for poly(dimethylene urethane) have been estimated. The first and the second cryoscopic constants have been calculated for dimethylene urethane. The experimental data obtained in the present work and literature findings on the heat capacity of the substances were used to calculate their thermodynamic functions: the heat capacity C° p ( T), enthalpy H°( T)− H°(0), entropy S°( T) and Gibbs function G°( T)− H°(0) over the range from T→0 to (370-480) K. Based on the data, the thermodynamic characteristics of polymerization process with five-membered ring opening Δ polH°, Δ polS° and Δ polG° of dimethylene urethane with the formation of linear partially crystalline poly(dimethylene urethane) have been evaluated. 相似文献
13.
Stannates Dy 2Sn 2O 7 and Ho 2Sn 2O 7 are produced by solid-phase synthesis from Dy 2O 3 (Ho 2O 3)–SnO 2 stoichiometric mixtures by calcining at 1473 K. The molar heat capacity of holmium and dysprosium stannates is measured by differential scanning calorimetry (DSC) in the temperature range 370–1000 K. The experimental data are used to calculate thermodynamic properties (enthalpy change H°( T)– H°(370 K), entropy change S°( T)– S°(370 K), and the reduced Gibbs free energy Φ°( T)) of the synthesized compound. 相似文献
14.
脂质体电动色谱是一种理想的评价药物与生物膜相互作用的模型. 在288~323 K范围内测定了中性芳香族溶质在脂质体电动色谱中的分配系数, 通过三项式拟合Van't Hoff图获得了一系列的热力学参数, 研究了溶质在脂质体电动色谱中的热力学分配行为. 结果表明, 分配系数随体系温度的升高和苯环所带亚甲基数目的增加而增大. 从288到323 K, Δ H>0, - TΔ S<0, Δ G<0, 溶质在脂质体电动色谱中的分配过程为熵驱动过程. 从288到298 K, 脂质体电动色谱分配系统的Δ Cp为负值, 其表现行为与经典疏水作用一致. 从303到323 K, 脂质体电动色谱分配系统的Δ Cp为正值, 其表现行为与经典疏水作用不完全吻合. Δ H和Δ S呈线性关系, 该分配系统存在焓熵补偿. 相似文献
15.
The calcium fluoride solid electrolyte Galvanic cell: (-) Pt, U 3O 8(s) + UO 2F 2(s) + BaUF 6(s) + BaF 2(s) | CaF 2(s) | NiO(s) + NiF 2(s), Pt (+) was used to measure the standard molar Gibbs energy of formation of BaUF 6(s). From the measured emf values of the cell and required Gibbs energy values from the literature, Δ f G m° ( T) of BaUF 6(s) has been calculated. The pseudo-binary phase diagram of BaF 2–UF 4 system was calculated by minimization of Gibbs energies of the phases present in the system. The stability domain of BaUF 6(s) has been calculated from the chemical potential diagram of Ba–U–F–O system at 800 K. 相似文献
16.
The phase equilibria for the reduction of SmMnO 3 with hydrogen were studied by the static method using a circulation vacuum setup in conjunction with XRD analysis of quenched solid phases. It was established that, over a temperature range of 973–1123 K and a pressure range of 10 ?10–10 ?16 Pa, SmMnO 3 dissociates by the reaction (1/2)Sm 2O 3 + MnO + (1/4)O 2; in this case, the temperature dependence of the equilibrium oxygen pressure and the Gibbs energy change can be described by the equations log $p_{O_2 } $ [Pa] = 25.35 ? 39150/ T ± 0.1, Δ G° T, kJ/mol = 187.62 ? 0.09 T ± 1.62, respectively. Based on the experimental data, the standard thermodynamic functions of formation of SmMnO 3 from elements were calculated: ΔH° T = ?1485.706 kJ/mol and Δ S° T = 244.39 J/(mol K). 相似文献
17.
The temperature dependences of the heat capacities of 5-vinyltetrazole and poly-5-vinyltetrazole were measured by adiabatic vacuum calorimetry over the temperature range 6-(350–370) K with errors of ~0.2%. The results were used to calculate the thermodynamic functions of the compounds, C p ° , H °( T) - H °(0), S °( T), and G °( T) - H °(0), over the temperature range from T → 0 to 350–370 K. The energy of combustion of 5-vinyltetrazole and poly-5-vinyltetrazole was measured in an isothermic-shell static bomb calorimeter. The standard enthalpies of combustion Δ c H ° and thermodynamic characteristics of formation Δ f H °, Δ f S °, and Δ f G ° at 298.15 K and p = 0.1 MPa were calculated. The results were used to determine the thermodynamic characteristics of polymerization of 5-vinyltetrazole over the temperature range from T → 0 to 350 K. 相似文献
18.
A new equation is suggested to define the temperature dependence of the Gibbs energy of hydration of hydrophobic substances: Δ G 0 = b 0 + b 1 T + b 2ln T. According to this equation, the hydration heat capacity is in inverse proportion to temperature. Consistent values of hydration heat capacity of nonpolar solutes have been obtained for different temperatures using data on solubility and dissolution enthalpy. The contributions of the hydrocarbon radicals and OH group to the heat capacity of hydration of the compounds were found for the temperature range 248–373 K. The hydration heat capacity of the hydroxyl group has a weak dependence on temperature and increases by only 12 J/(mol·K) in the specified temperature interval. Changes in the hydration entropy of hydrophobic and OH groups are calculated for the temperature increasing from 248 K to 373 K. 相似文献
19.
Summary The thermodynamic data for NZP compounds MZr 2(PO 4) 3 ( M=Na, K, Rb, Cs, Zr 0.25) and Na 5D(PO 4) 3 ( D=Ti, Zr) are reported. The heat capacities of the phosphates were measured between T=7 and T=640 K. The standard enthalpies entropies, and Gibbs functions of formation at T=298.15 K were derived. The obtained thermodynamic characteristics of phosphates of the NZP type structure and literature data are summarized. Thermodynamic functions of reactions of solid-state synthesis were calculated and the usability of ceramic technology for obtaining NZP compounds was proved. 相似文献
20.
The vaporization of pure RbCl, GdCl 3, and RbCl‐GdCl 3 samples of different phase compositions was investigated in the temperature range between 666 K and 982 K by use of the Knudsen effusion mass spectrometry. The gaseous species RbCl, Rb 2Cl 2, GdCl 3, and RbGdCl 4 were identified in the equilibrium vapours and their partial pressures were determined. The enthalpy of dissociation of RbGdCl 4(g), Δ dissH°(859 K) = 263.1 ± 7.7 kJ mol —1, was evaluated by second law treatment of the equilibrium partial pressures. The thermodynamic activities of RbCl and GdCl 3 were obtained at 800 K in the two‐phase fields {Rb 3GdCl 6(s) + liquid} and {RbGd 2Cl 7(s) + GdCl 3(s)}. The Gibbs free energies of formation of the pseudo‐binary phases Rb 3GdCl 6(s), Δ fG°(800 K) = —75.1 ± 2.5 kJ mol —1 and RbGd 2Cl 7(s), Δ fG°(800 K) = —40.6 ± 1.2 kJ mol —1, were evaluated from the thermodynamic activities of the components. The results are compared with the available literature data. 相似文献
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