K is for constant

Almost every middle and high school student has seen a chemical equation written out. When they imagine what that looks like, they probably know an equation filled with letters that have one arrow in the middle. However, most chemical equations actually have two arrows because they are equilibrium reactions. An equilibrium reaction is a reaction in which reactants and products are being created at an equal rate, hence equilibrium. This does not mean that the same amount of reactants and products are created, just that they are created at the same rate, or speed. To understand the amount of reactants and products created when a reaction reaches equilibrium, the constant, K, is used.

The equilibrium constant is determined by the ratio of the concentration of the products and the concentration of reactants. Some of the most common equilibrium constants are for acids and bases, as those are the most commonly occurring equilibrium reactions. The constant for an acid will always involve the concentration of hydrogen ions and hydroxide ions for bases. Since water dissociates into hydrogen and hydroxide, it also has a K value that remains constant at 10^-14. While K never has units, the magnitude of the number can say a lot about an equation. A very large K value means that way more products than reactants are being produced and the other way around for a small value. Given that equilibrium reactions occur everyday, in and out of the lab, understanding how they work is very important. Whether it be the air we breathe or the water we drink, almost everything is at an equilibrium.