# A Direct Entropic Approach to the Thermal Balance of Spontaneous Chemical Reactions

## TL;DR

This paper introduces a new way to understand how heat is balanced in chemical reactions by focusing on entropy and its redistribution.

## Contribution

The paper proposes a direct entropic approach to model thermal balances in chemical reactions using entropy and chemical potential.

## Key findings

- A model of exothermic and endothermic reactions is developed using entropy and chemical potential.
- Numerical examples demonstrate the application of the direct entropic approach.
- The approach is connected to traditional models of thermal balance in chemical reactions.

## Abstract

When working with, and learning about, the thermal balance of a chemical reaction, we need to consider two overlapping but conceptually distinct aspects: one relates to the process of reallocating entropy between reactants and products (because of different specific entropies of the new substances compared to those of the old), and the other to dissipative processes. Together, they determine how much entropy is exchanged between the chemicals and their environment (i.e., in heating and cooling). By making explicit use of (a) the two conjugate pairs chemical amount (i.e., amount of substance) and chemical potential, and entropy and temperature, respectively, (b) the laws of balance of amount of substance on the one hand and entropy on the other, and (c) a generalized approach to the energy principle, it is possible to create both imaginative and formal conceptual tools for modeling thermal balances associated with chemical transformations in general and exothermic and endothermic reactions in particular. In this paper, we outline the concepts and relations needed for a direct approach to chemical and thermal dynamics, create a model of exothermic and endothermic reactions, including numerical examples, and discuss how to relate the direct entropic approach to traditional models of these phenomena.