Chapter 12 – Chemical Equilibrium and Dissociation

Methods by which realistic combustion processes, with dissociation, can be calculated are developed using the techniques described in previous chapters. The concept of chemical potential, the driving force towards chemical equilibrium, is introduced. Then equations exhibiting dissociation are developed, culminating in a generalised equation for the combustion of C x H y . The law of mass action is used to derive the equilibrium constant, K p . It is shown that equilibrium is achieved at the minimum Gibbs energy of the mixture. The van't Hoff relationship is derived and this provides a method for evaluating the energy of reaction from the equilibrium constant. These data are then used to evaluate the effect of temperature and pressure on the degree of dissociation of reactions. Finally, this approach is used to show that the temperatures achieved during combustion will generally result in nitric oxide in the equilibrium products. The chapter is concluded with a number of worked examples showing the method of calculating combustion processes with dissociation.