THE DEVIATIONS FROM THE LAW OF MASS ACTION FOR SIMPLE BIMOLECULAR REACTIONS: MOLECULAR DYNAMICS STUDY.

The influence of concentrations of reagents on the rate of reaction: A + B → C + B has been investigated by performing large scale computer simulations on systems of spherically symmetric molecules. The problem has been analyzed both for deterministic systems (gas, liquid) and for the stochastic ones where the particles are immersed in the Brownian medium. Significant deviations from the law of mass action have been found. The deviations result not only from fluctuations in concentrations of reagents. For the Brownian systems the simulations have given a positive value of the excess in the rate coefficient even for very long times, which contradicts with general expectations. The reason for the positive excess values is repulsion between B particles (the so called excluded volume effect). The effect is strongly influenced by the shape of the probability density function for B-B pairs. As a result, for the liquids the effect is weaker: for short times the excess in rate coefficient is positive but for long times it becomes negative. [ABSTRACT FROM AUTHOR]