ABSTRACT
The equilibrium constant (K) and the Gibbs energy of a reaction (∆r G°) both provide metrics for quantifying a reaction, but neither quantity can explain why a reaction happens. Reactions happen because electrons move to become more stable, lower energy. This movement can be the reshuffling of how electrons are shared, with no net transfer of electrons from one atom to another. To understand this reshuffling of shared electrons, acid–base chemistry is used as a framework. There are three commonly used acid–base definitions (Arrhenius, Brønsted-Lowry, and Lewis) and this chapter focuses on the Brønsted-Lowry and Lewis acid–base definitions. These theoretical frameworks provide a means of identifying the role that is being played by chemicals in a reaction, and acidity constant (K a) values provide a means of understanding the likelihood that a compound will share, or not share, its electrons. Acidity constants are then used to help explain trends in acidity, including atomic size, electronegativity, hybridization, charge, and delocalization. The chapter concludes by introducing readers to pH and buffers, both of which play important roles in chemistry and biochemistry.
