ABSTRACT
Nature is inherently heterogeneous, and consequently, natural processes occur in a direction that lead to homogeneity and equilibrium. This is essentially a restatement of the second law of thermodynamics. In the previous chapter we assumed that fuels react with oxygen to produce CO
, H
O, and other products. We now ask the question whether these products, e.g., CO
and H
O, can react among themselves to give back the fuel and molecular oxygen. If they cannot, then we must answer the questions, “Why not? What governs the direction of a chemical reaction? Why do reactions stop prior to completion, i.e., complete consumption of the reactants? Can we predict the composition of the products if reactions are not completed?” The direction of heat flow is determined by a temperature gradient, or thermal potential, and that of fluid flow by a pressure gradient, or mechanical potential. In this chapter we will characterize the predominant parameters that govern the direction of a chemical reaction. We will learn that the gradient of the Gibbs energy, or chemical potential, determines the direction in which a chemical reaction proceeds. We will also discuss the composition of reaction products under equilibrium conditions.
