On the sum of chemical reactions

• Published in: European journal of applied mathematics Vol. 34; no. 2; pp. 303 - 325
• Main Authors: HOESSLY, LINARD, WIUF, CARSTEN, XIA, PANQIU
• Format: Journal Article
• Language: English
• Published: Cambridge Cambridge University Press 01.04.2023
• Subjects: Applied mathematics; Chemical reactions; Gene expression; Photosynthesis; Proteins
• ISSN: 0956-7925; 1469-4425
• DOI: 10.1017/S0956792522000146

It is standard in chemistry to represent a sequence of reactions by a single overall reaction, often called a complex reaction in contrast to an elementary reaction. Photosynthesis $6 \text{CO}_2+6 \text{H}_2\text{O} \longrightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6 \text{O}_2$ is an example of such complex reaction. We introduce a mathematical operation that corresponds to summing two chemical reactions. Specifically, we define an associative and non-communicative operation on the product space ${\mathbb{N}}_0^n\times {\mathbb{N}}_0^n$ (representing the reactant and the product of a chemical reaction, respectively). The operation models the overall effect of two reactions happening in succession, one after the other. We study the algebraic properties of the operation and apply the results to stochastic reaction networks (RNs), in particular to reachability of states, and to reduction of RNs.