Science Fair Project Encyclopedia
|Internal energy||U||The energy needed to create a system|
|Helmholtz free energy||F = U - TS||Also represented by A|
|Enthalpy||H = U + PV|
|Gibbs free energy||G = U + PV - TS|
The following differential relations hold for the four potentials:
If we write the above four equations generally as
Then it is seen that
yielding expressions for T, P, S, and V in terms of derivatives of the potentials
Furthermore, mathematically we have
which are known as Maxwell's relations
Changes in these quantities are useful for assessing the degree to which a chemical reaction will proceed. The relevant quantity depends on the reaction conditions, as shown in the following table. Δ denotes the change in the potential and at equilibrium the change will be zero.
|Constant V||Constant P|
Most commonly one considers reactions at constant P and T, so the Gibbs free energy is the most useful potential in studies of chemical reactions.
- Lewis, Gilbert Newton; Randall, Merle; Revised by Pitzer, Kenneth S. & Brewer, Leo "Thermodynamics" 2nd Editon, New York, NY USA: McGraw-Hill Book Co. 1961.
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details