Investigation Of The Effect Of The Size Of Reactants On The Heterogeneous Reactions

The effect of particle size of reactants in heterogeneous systems on chemical thermodynamics and kinetics were reviewed in this paper, the research contents were put forward, the academic significance involving this work was elaborated and the prospects of application and the developing trends of nanoparticles as reactants in chemical fields were forecasted. At present, it is found that there are obvious effects of particle size of reactants in non-catalysis heterogeneous reactions studies on the standard equlibrium constants, but the reports on the regularity of effect of the reactant size on the standard equlibrium constants haven't been discovered so far. Some scientists have in theory studied the effects of reactant sizes on kinetics of heterogeneous reactions and have brought forward many shrinking-core models with different forms in non-catalysis heterogeneous reactions studies. But the kinetic equations reported are mainly limited to some experiential or semiexperientialkinetic models, it isn't reported that the relations of the kinetic parameters to reactant sizes and that the effect of reactant size on the reaction order, and it isn't reasonably explained that the reactant size may result in the apparent activation energy and the pre-exponential factor decreasing. Therefore, it is necessary to investigate deeply thermodynamics and kinetics of the non-catalysis heterogeneous reactions involving nano-reactants.Firstly, the heterogeneous reaction systems used for the studies, reactions of nano-CuO and nano-ZnO with sodium bisulfate respectively, were selected in this work. Secondly, the nanoparticles with different sizes were preparated by using the liquid phase reaction and the solid phase reaction. Finally, the regularities of effects of the reactant size on the standard equilibrium constants and thermodynemic properties in heterogeneous reactions were firstly investigated, at the same time the theoretical models of the heterogeneous reaction was established and the regularities of effects of the reactant size on kinetic parameters were also investigated, and these regularities were discussed.The nano-CuO and nano-ZnO with different sizes were prepared in this work, and then the reactants were reacted with NaHSC>4 at differenttemperatures, so the standard equilibrium constant and the standard Gibbs free energy of the reactions with the different reactant sizes can be calculated by using the concentrations of H* and Cu2+or Zn + in the equilibrium solution, whereas the standard molar enthalpy and the standard molar entropy for reaction can also be calculated by use of the curve equations of ArG* -T, thus the regularities of the standard equilibrium constant, the standard molar Gibbs free energy, the standard molar enthalpy and the standard molar entropy for reaction varying with the sizes of reactants were obtained. The instantaneous concentrations of products were determined by a auto-recording ion meter or atomic absorption spectrometry at regular intervals, and then the regularities of the reaction rate constant, the apparent activation energy, the pre-exponential factor and the reaction order varying with the reactant sizes were acquired. Main conclusions are showed as follows:(1) The nanoparticles with different sizes can be prepared by the liquid reaction and the solid reaction, the average sizes of nano-CuO and nano-ZnO prepared are 10 to 24nm and 22 to 70nm respectively.(2) There are obvious effects of the reactant size on the standard equilibrium constant, the standard molar Gibbs free energys, thestandard molar enthalpy, the standard molar entropy, the reaction rate constant, the apparent activation energy, the pre-exponential factor and the reaction order.(3) The standard equilibrium constant is not only the function of the temperatures, but also is related to the sizes of the reactant. The standard equilibrium constant increase, whereas the standard Gibbs free energy, the standard molar enthalpy and the standard molar entropy decrease with the reactant size decreasing.(4) The apparent activation energy and the pre-exponential factor decrease, whereas the reaction rate constant and the reaction order increase with the reactant sizes decreasing, and there are better linear relations of the reaction rate constants at different temperatures and the apparent activation energy to the reciprocal of the reactant sizes, the explanation of the effects of reactant size on the apparent activation energy and the pre-exponential factor was given satisfactorily.