These balanced two-way reactions occur all around and even in us. For example, they occur in our blood, where the reaction between carbon dioxide and water forms carbonic acid $$\ce{(HCO3- )}$$ (Figure $$\PageIndex{1}$$). Human physiology is adapted to the amount of ionized products produced by this reaction ($$\ce{HCO3-}$$ and H+). In this chapter, you will learn how to predict the position of the balance and the yield of a product of a reaction under specific conditions, how to change a reaction's conditions to increase or reduce yield, and how to evaluate an equilibrium system's reaction to disturbances.