What is Gibbs energy?

The spontaneous nature of processes insystems of open and closed types 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 secondthermodynamic 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 Gibbs energy level to the value that occurs when it reaches a steady 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 temperature and pressure unchanged, 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 by 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 temperaturethermodynamic; H is the 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), while a low one leads to a decrease in the ordered state of the system (disorder).

Since both the Gibbs energy and the enthalpy are one of thefunctions of the system in thermodynamics, then by changing G or H one can characterize the ongoing chemical transformations. If the equation of reaction and the change in Gibbs energy are given, then it is classed as thermochemical.

Applicable to this energy may beThe Hess rule is formulated: if the pressure and temperature are unchanged, 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 that take place and their quantity do not influence the result.

Since the energy, referred to in the article,is a variable quantity, then 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 tothe system is externally affected (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 we are talking about ex- ergonic manifestations.

The concept of Gibbs energy found the widestapplication 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.