Signup now and receive and email once I publish new content.
Screenshot of Interactive multimedia showing relationship between free energy and the equilibrium constant (click to enlarge)
A + 2 B ⇄ 3 C |
![]() |
While future sections discuss how to determine which products and reactants appear in the equilibrium expression, the power of the equilibrium constant is worth further exploration. The constant has two different forms, variable and numeric with each being useful in different ways.
The variable form of K is generic in the sense that it implies equilibrium of a specific reaction under specific conditions but does not imply anything about the equation itself. Subscripts are used to give information about the type of reaction and/or the states of the species involved.
KÂ Â Â Â Â Â Â Â Generic, species can be entered in a variety forms.
Kc       All species must be entered as molar concentrations, generally all aqueous.
Kp       All species are gases and entered as partial pressures.
Ka       Reaction is an acid ionization with molar concentrations.
Kb         Reaction is a base dissociation with molar concentrations
Ksp      Reaction is for a solid dissolving with molar concentrations.
If the specific equilibrium system is known, one that has a subscript, reference tables can be consulted for specific numeric data. The generic form though has limitless possibilities and there is no reference data available. However, it is sometimes possible to manipulate the specific equilibrium systems and their values to determine the equilibrium constant of a generic equation.
While the numeric form is useful for many purposes, three are of particular interest. First, the actual value of the constant shows which side of the equation is favored with K >1 favoring products and K < 1 favoring reactants. The magnitude of the value also indicates how much it favors one or the other with values much greater or less than one actually going out of equilibrium.
Secondly, because it is a constant under specific conditions, concentrations can be changed or predicted using the equilibrium expression.
Finally, it can be related to free energy and therefore spontaneity using ∆G = -RTlnK. Variations can also be used for systems that are not under equilibrium conditions as will be discussed in future sections.
Overall, this part of the textbook offers a wonderful review of the history of equilibrium and those that discovered it, with the addition of a look at the power of the equilibrium constant.
Signup now and receive and email once I publish new content.