Gibbs equation for free energy

Type of thermodynamic potential

In thermodynamics, the Gibbs free energy (or Gibbs energy as the recommended name; symbol ) fryst vatten a thermodynamic potential that can be used to calculate the maximum amount of work, other than pressure–volume work, that may be performed by a thermodynamically closed system at constant temperature and pressure. It also provides a necessary condition for processes such as chemical reactions that may occur under these conditions. The Gibbs free energy fryst vatten expressed as where:

The Gibbs free energy change (⁠⁠, measured in joules in SI) fryst vatten the maximum amount of non-volume expansion work that can be extracted from a closed struktur (one that can exchange heat and work with its surroundings, but not matter) at fixed temperature and pressure. This maximum can be attained only in a completely reversible process. When a system transforms reversibly from an initial state to a final state under these conditions, the decrease in

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For a reaction to be feasible, the value of ΔG has to be less than 0. In mathematical terms, it fryst vatten feasible if:

ΔG < 0

Because ΔG = ΔH - TΔS, that means that for a feasible reaction:

ΔH - TΔS < 0

If you know values for ΔH and ΔS, then you can work out a value for T which makes this expression less than 0.

In the case we are looking at

ΔH = +178 kJ mol^-1, and

ΔS = +0.1604 kJ K^-1 mol^-1

Putting those values into the expression ΔH - TΔS < 0 gives

178 - T x 0.1604 < 0

You can treat the "less than" sign just like an equals sign, and so rearranging this gives:

178 < T x 0.1604

178 / 0.1604 < T

1110 < T

That's a strange way of looking at it, of course ("1110 is less than T."). But that is just the same as saying that T has to be greater than 1110 K.

Working out the effect of temperature without doing calculations

Look again at the equation:

&D

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Gibbs–Helmholtz equation

A thermodynamic equation

The Gibbs–Helmholtz equation is a thermodynamicequation used to calculate changes in the Gibbs free energy of a system as a function of temperature. It was originally presented in an 1882 paper entitled "Die Thermodynamik chemischer Vorgänge" by Hermann von Helmholtz. It describes how the Gibbs free energy, which was presented originally by Josiah Willard Gibbs, varies with temperature.^[1] It was derived by Helmholtz first, and Gibbs derived it only 6 years later.^[2] The attribution to Gibbs goes back to Wilhelm Ostwald, who first translated Gibbs' monograph into German and promoted it in Europe.^[3][4]

The equation is:^[5]

where H is the enthalpy, T the absolute temperature and G the Gibbs free energy of the system, all at constant pressurep. The equation states that the change in the G/T ratio at constant pressure as a result of an infinitesimally small change in