Quick question about Gibbs free energy

In summary, the expression defining Gibbs free energy is G = U - TS + pV. T and p refer to the temperature and pressure of the system, not the environment. For the Gibbs free energy to be defined, the system must be in thermal and mechanical equilibrium with the environment, meaning it is surrounded by heat and pressure reservoirs. In this case, the Gibbs free energy is at its minimum value. The confusion may arise from the fact that the work to give the system a final volume V at constant pressure p should be equal to pV from the surroundings.
  • #1
Zarquon
20
0
In the expression defining Gibbs free energy,
G = U - TS +pV,
are T and p the temperature and pressure of the environment, or of the system itself? Or is it a requirement that the system has the same temperature and pressure as the environment for the Gibbs free energy to be defined?
 
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  • #2
T and p describe the system. For a system in thermal equilibirum and mechanical equilibrium with the environment - consider the system surrounded by heat and pressure reservoirs - the Gibbs free energy is at its minimum value.
 
  • #3
Thanks.
Part of the reason for my confusion is this page:
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/helmholtz.html
Seems to me that the "work to give the system final volume V at constant pressure p" should be equal to pV where p is the pressure from the surroundings?
 

1. What is Gibbs free energy?

Gibbs free energy, also known as Gibbs energy, is a thermodynamic quantity that measures the energy available in a system to do useful work. It is denoted by the symbol G and is named after American scientist Josiah Willard Gibbs.

2. How is Gibbs free energy related to enthalpy and entropy?

Gibbs free energy is related to enthalpy and entropy through the equation G = H - TS, where H is enthalpy, T is temperature in Kelvin, and S is entropy. This equation is also known as Gibbs-Helmholtz equation.

3. What is the significance of Gibbs free energy in chemical reactions?

Gibbs free energy helps in predicting whether a chemical reaction will be spontaneous or non-spontaneous. If the value of G is negative, the reaction is spontaneous, and if it is positive, the reaction is non-spontaneous. A value of zero indicates that the reaction is at equilibrium.

4. Can Gibbs free energy be negative?

Yes, Gibbs free energy can be negative. A negative value indicates that the reaction is spontaneous, meaning it will occur without the input of external energy. This usually happens when the change in entropy is positive and the change in enthalpy is negative.

5. How is Gibbs free energy used in practical applications?

Gibbs free energy is used in various fields such as chemistry, physics, and engineering to understand and predict the behavior of systems. It is also used in the design of chemical processes and in the study of biological systems, such as metabolism and cell signaling.

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