Login processing...

Trial ends in Request Full Access Tell Your Colleague About Jove

17.6: Gibbs Vrije Energie
INHOUDSOPGAVE

JoVE Core
Chemistry

A subscription to JoVE is required to view this content. You will only be able to see the first 20 seconds.

Education
Gibbs Free Energy
 
TRANSCRIPT

17.6: Gibbs Free Energy

One of the challenges of using the second law of thermodynamics to determine if a process is spontaneous is that it requires measurements of the entropy change for the system and the entropy change for the surroundings. An alternative approach involving a new thermodynamic property defined in terms of system properties only was introduced in the late nineteenth century by American mathematician Josiah Willard Gibbs. This new property is called the Gibbs free energy (G) (or simply the free energy), and it is defined in terms of a system’s enthalpy and entropy as the following:

Eq1

Free energy is a state function, and at constant temperature and pressure, the free energy change (ΔG) may be expressed as the following:

Eq2

The relationship between this system property and the spontaneity of a process may be understood by recalling the previously derived second law expression:

Eq3

The first law requires that qsurr = −qsys, and at constant pressure qsys = ΔH, so this expression may be rewritten as:

Eq4

Multiplying both sides of this equation by −T and rearranging yields the following:

Eq5

For simplicity’s sake, the subscript “sys” can be omitted, and the expression becomes

Eq6

Comparing this equation to the previous one for free energy change shows the following relation:

Eq7

The free energy change is, therefore, a reliable indicator of the spontaneity of a process, as it is directly related to the previously identified spontaneity indicator, ΔSuniv.

If ΔSuniv > 0, ΔG < 0 and the reaction is spontaneous.

If ΔSuniv < 0, ΔG > 0 and the reaction is nonspontaneous.

If ΔSuniv = 0, ΔG = 0 and the reaction is at equilibrium.

This text is adapted from Openstax, Chemistry 2e, Chapter 16.4: Free Energy.

Get cutting-edge science videos from JoVE sent straight to your inbox every month.

Waiting X
simple hit counter