Search results for "chemical equilibrium"
showing 10 items of 27 documents
Partial molar enthalpies and reaction enthalpies from equilibrium molecular dynamics simulation
2014
We present a new molecular simulation technique for determining partial molar enthalpies in mixtures of gases and liquids from single simulations, without relying on particle insertions, deletions, or identity changes. The method can also be applied to systems with chemical reactions. We demonstrate our method for binary mixtures of Weeks-Chandler-Anderson particles by comparing with conventional simulation techniques, as well as for a simple model that mimics a chemical reaction. The method considers small subsystems inside a large reservoir (i.e., the simulation box), and uses the construction of Hill to compute properties in the thermodynamic limit from small-scale fluctuations. Results …
Kinetics and Mechanism of the Nucleophilic Substitution of Tellurium(II) Dialkanethiolates, Te(SR1)2 with Thiols, HSR2
2005
The equilibrium reaction between tellurium(II) dithiolates and thiols, Te(SR1)2 + 2 HSR2 ⇌ Te(SR2)2 + 2 HSR1 was studied by means of 1H- and 125Te NMR spectroscopy and ab initio quantum chemical methods. It was found that the reaction is catalyzed by Bronsted acids and bases, the catalytic activity corresponding to the strength of the respective acid or base. Investigation of the initial step of the reaction, Te(SR1)2 + HSR2 ⇌ Te(SR1)(SR2) + HSR1, showed it to proceed according to first order kinetics for Te(SR1)2, HSR2 and for the catalyst. Ab initio geometry optimizations and frequency calculations suggest [Te(SR1)(HSR1)(HSR2)]+ and [Te(SR1)2(SR2)]− to be stable intermediates and not tran…
Chemical heterogeneities in the mantle: The equilibrium thermodynamic approach
2016
Abstract This study attempts to answer a simple and yet fundamental question in relation to our understanding of the chemical evolution of deep Earth and planetary interiors. Given two initially separate assemblages (lithologies) in chemical equilibrium can we predict the chemical and mineralogical compositions of the two assemblages when they are put together to form a new equilibrated system? Perhaps a common perception is that given sufficient time, the two assemblages will homogenize chemically and mineralogically, however from a chemical thermodynamic point of view, this is not the case. Certain petrological differences in terms of bulk composition, mineralogy and mineral abundance rem…
Equation of state of strongly interacting matter and intensity interferometry of thermal photons
2011
Abstract We find that an equation of state (EOS) for hot hadronic matter consisting of all mesons (baryons) having M 1.5 ( 2.0 ) GeV along with Hagedorn resonances in thermal and chemical equilibrium, matches rather smoothly with lattice EOS ( p 4 action, N τ = 8 ) for T up to ≈200 MeV, when corrections are made for the finite volume of hadrons. Two equations of state, HHL and HHB are constructed where the above is matched to the lattice and bag model EoS respectively at a critical temperature T c = 165 MeV . We find that the particle and thermal photon spectra differ only marginally for the two equations of state at both RHIC and LHC energies. The intensity interferometry results, speciall…
Equation of state of strongly interacting matter: spectra for thermal particles and intensity correlation of thermal photons
2010
We find that an equation of state for hot hadronic matter consisting of all baryons having $M < 2$ GeV and all mesons having $M < 1.5$ GeV, along with Hagedorn resonances in thermal and chemical equilibrium, matches rather smoothly with lattice equation of state (p4 action, ${N_��}=8$) for T up to $\approx 200$ MeV, when corrected for the finite volume of hadrons. Next we construct two equations of state for strongly interacting matter; one, HHL, in which the above is matched to the lattice equation of state at $T=165$ MeV and the other, HHB, where we match it to a bag model equation of state with critical temperature $T_c=165$ MeV. We compare particle spectra, thermal photon spectra …
Variation of extent of reaction in closed chemical equilibrium when changing the temperature at constant volume
2011
In this paper it is presented a thermodynamic analysis that aims to find the mathematical expression of the variation of extent of reaction with the infinitesimal variation in the temperature at constant volume of a chemical equilibrium mixture. The goal of this paper is to establish an alternative approach to avoid both the Le Chatelier's principle and the problems that emerge when trying to apply its qualitative statements. This attempt is based on the laws of thermodynamics.
Modelling biological and chemically induced precipitation of calcium phosphate in enhanced biological phosphorus removal systems
2011
The biologically induced precipitation processes can be important in wastewater treatment, in particular treating raw wastewater with high calcium concentration combined with Enhanced Biological Phosphorus Removal. Currently, there is little information and experience in modelling jointly biological and chemical processes. This paper presents a calcium phosphate precipitation model and its inclusion in the Activated Sludge Model No 2d (ASM2d). The proposed precipitation model considers that aqueous phase reactions quickly achieve the chemical equilibrium and that aqueous-solid change is kinetically governed. The model was calibrated using data from four experiments in a Sequencing Batch Rea…
Mechanical unfolding pathway of a model β-peptide foldamer.
2015
Foldamers constructed from oligomers of β-peptides form stable secondary helix structures already for small chain lengths, which makes them ideal candidates for the investigation of the (un)folding of polypeptides. Here, the results of molecular simulations of the mechanical unfolding of a β-heptapeptide in methanol solvent revealing the detailed unfolding pathway are reported. The unfolding process is shown to proceed via a stable intermediate even for such a small system. This result is arrived at performing non-equilibrium force ramp simulations employing different pulling velocities and also using standard calculations of the potential of mean force, i.e., the free energy as a function …
Kinetico-mechanistic studies of the acidolysis of Rh-C bonds in monocyclometallated dirhodium(II) acetato complexes; influence of electronic and ster…
2011
The protonation/demetallation reaction, in CD(3)COOD, of phosphine monometallated triacetato-bridged dirhodium(ii) complexes of general formulae [Rh(2)(μ-OOCCH(3))(3){(RC(5)CH(3))P(RC(6)H(4))(2)}(2)] has been studied from a kinetico-mechanistic perspective. The process has been monitored via the disappearance of the nuclear magnetic resonance signals of the protons present in the non-metallated ortho positions of the phosphine ligand and taking advantage of the relatively fast back metallation process that follows the acidolysis reaction, the sequence behaving as an overall equilibrium reaction. The process has a high associative character with important entropy demands, increasing both for…
Determination of cluster binding energies on metal surfaces by statistics
2000
Abstract Two simple formulae to determine binding energies of two-dimensional clusters on surfaces in thermal equilibrium are derived. One requires measurement of monomer and cluster populations and of the surface temperature. The cluster dissociation rate is derived and related to the atom hopping rate, allowing the theory to be extended to adatom populations that are not in chemical equilibrium. The result gives a recipe for determining dissociation energies that requires measurements of only two rates at a single temperature.