Fundamental Bioengineering

9Chemical Thermodynamics Applied in Bioengineering

John Villadsen

Summary

The analysis of bioreactions in Chapters 4, 7, and 8 is incomplete without including the thermodynamics of the reactions. The chemical equilibrium determines how far a reaction will convert substrates to products, and the heat of reaction must be determined in order to design heat exchangers. Here, the most important elements of chemical thermodynamics are reviewed. After definition of the state functions of thermodynamics and showing how thermodynamic properties can be calculated from tables, the feasibility of the EMP pathway from glucose to pyruvate is discussed and the importance of having large values of (−ΔG_R) for the first and last reactions in a pathway is noted. Examples of calculations of (−ΔG_R) for a number of biochemical reactions are given, first using thermodynamic tables and next using the methods of electrochemistry. The exceedingly complicated energy transformation from reduced substrates to ATP in mitochondria is reviewed. Finally, simple methods for calculation of the heat of reaction of bioreactions are discussed. These methods are based on the same principles as was used in the redox balances of Chapter 3, and their application is illustrated by several examples.

9.0 Introduction

Equilibrium thermodynamics is concerned with systems that are in equilibrium. The saturation concentration $s_{\mathrm{o}}^{*}$ of oxygen in an aqueous phase sparged with air of a given partial pressure π_O2 of O₂ is primarily ...