ABSTRACT
Entropy, along with enthalpy, provides a means of determining whether a reaction is favored in the forward direction or in the reverse direction. But exothermic reactions, enthalpically product favored, can be entropically reactant favored, concentrating energy and matter. In these reactions, then, how can one determine whether a reaction will proceed toward products or stay as reactants? Gibbs energy (∆r G°), a composite of enthalpy and entropy, provides a clear framework for determining whether a reaction is reactant favored or product favored, and how changes in temperature will affect the position of the reaction. Finally, readers are introduced to the idea of coupled reactions, where an exergonic (energy producing) reaction is combined with an endergonic (energy consuming) reaction. Examples are given in the context of biochemistry (ATP hydrolysis to drive metabolic change) and metallurgy (the oxidation of coal and hydrogen to reduce metals) to underscore the importance of coupled reactions.
