What is Gibbs energy?

The spontaneous nature of processes in open and closed systems is described through a special criterion called the Gibbs energy. It is a function of the state. D.W. Gibbs, working with thermodynamic systems, managed to deduce it through entropy and enthalpy. Gibbs energy, in particular, makes it possible to predict the direction of the flow of spontaneous biological processes and to evaluate their theoretically achievable efficiency.

If we apply Gibbs' conclusions to the second thermodynamic law, the formulation will be as follows: for constant (const) pressure and temperature without external influence, the system can support the spontaneous flow of only such processes, the consequence of which is the decrease in the level of Gibbs energy to the value that occurs when it reaches a steady state Minimum. The equilibrium of any thermodynamic system means the invariance of this energy (minimum). Therefore, Gibbs energy is a potential (free enthalpy) in isobaric-isothermal systems. Let us explain why the minimum is specified. The fact is that this is one of the most important postulates of equilibrium in thermodynamics: this state with the invariance of temperature and pressure means that for the next change it is necessary to increase the energy level, and this is possible only if some external factors change.

The letter designation is G. Numerically equal to the difference between the known enthalpy and the value of the product of temperature on entropy. That is, Gibbs energy can be expressed through the following formula:

G = H - (S * t),

Where S is the entropy of the system; T is the thermodynamic temperature; H - enthalpy. The entropy of the system in this formula is included in order to take into account the fact that a high temperature leads to a decrease in the ordered state of the system (disorder), and a low one - on the contrary.

Since both the Gibbs energy and the enthalpy are one of the functions of the system in thermodynamics, it is possible to characterize the chemical transformations that take place by changing G or H. If the equation of reaction and the change in Gibbs energy are given, then it is referred to the class of thermochemical.

With regard to this energy, the Hess Rule can be formulated: if the pressure and temperature are unchanged, then the creation of new substances from the initial (basic reagents) leads to the fact that the energy in the system changes, while the type of reactions occurring and their number do not influence the result.

Since the energy described in the article is a variable quantity, the concept of "standard Gibbs energy" was introduced to perform the calculations. This value is present in any chemical reference book, numerically equal to 298 kJ / mol (note that the dimension is exactly the same as for any other molar energy). This value allows you to calculate the change for almost any chemical process.

If during the course of the chemical reaction to the system there is an external effect (work is done), then the value of Gibbs energy increases. Such reactions are referred to as endergonic. Accordingly, if the system itself does work, expending energy, then it is about ex-ergonomic manifestations.

The concept of Gibbs energy has found wide application in modern chemistry. For example, the synthesis of polymers is based on the addition reactions. When they are carried out, several particles are combined into one, while the value of entropy decreases. Based on the Gibbs formula, it can be argued that an external action (for example, a high-temperature one) can reverse such an exothermic addition reaction, which is confirmed in practice.