Universal dynamic scaling in chemical reactions at and away from equilibrium

TL;DR

This paper establishes universal dynamic scaling laws for fluctuations in thermodynamic observables in chemical reactions, both at and away from equilibrium, through analytical and numerical methods, revealing classes based on reaction mechanisms and conditions.

Contribution

It introduces two complementary approaches to dynamic scaling in chemical reaction fluctuations and classifies reaction mechanisms according to their scaling behaviors and universality classes.

Findings

Scaling laws confirmed by analytical and numerical methods.

Reaction classes organized by molecularity, vessel type, and equilibrium state.

Feedback reactions can shift between classes with parameter changes.

Abstract

Physical kinetic roughening processes are well known to exhibit universal scaling of observables that fluctuate in space and time. Are there analogous dynamic scaling laws that are unique to the chemical reaction mechanisms available synthetically and occurring naturally? Here, we formulate two complementary approaches to the dynamic scaling of stochastic fluctuations in thermodynamic observables at and away from equilibrium. Both analytical expressions and numerical simulations confirm our dynamic scaling ans{\"a}tze with their associated exponents, functions, and laws. A survey of common chemical mechanisms reveals classes that organize according to the molecularity of the reactions involved, the nature of the reaction vessel and external reservoirs, (non)equilibrium conditions, and the extent of autocatalysis in the reaction network. Coupled reactions capable of chemical feedback can transition, sometimes sharply, between these classes with the variation of experimental parameters such as temperature. While path observables like the dynamical activity have scaling exponents that are time-independent, fluctuations in the entropy production and flow can have time-dependent scaling exponents and self-averaging properties as a result of temporal correlations that emerge during thermodynamically irreversible processes. Altogether, these results establish dynamic universality in the nonequilibrium fluctuations of thermodynamic observables for well-mixed chemical reactions.