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Chemical Thermodynamics

Chemical thermodynamics

Chemical thermodynamics is the study of the interrelationship of heat and work with chemical reactions or with physical changes of state within the limits of the laws of thermodynamics.

Chemical thermodynamics involves not only laboratory measurements of various thermodynamic properties, but also the application of mathematical methods to the study of chemical issues and the spontaneity of processes.

The structure of chemical thermodynamics is based on the first two laws of thermodynamics. From the first and second laws of thermodynamics, four equations called "fundamental Gibbs equations" can be derived. From these four, a multitude of equations relating the thermodynamic properties of the thermodynamic system can be derived using relatively simple mathematics. This describes the mathematical framework of chemical thermodynamics.

Chemical thermodynamics is in close contact with sections of chemistry such as

  • analytic chemistry
  • electrochemistry
  • colloid chemistry
  • Adsorption and chromatography

What Is Chemical Thermodynamics Used For?

The main objective of chemical thermodynamics is the establishment of a criterion to determine the feasibility or spontaneity of a given transformation. In this way, chemical thermodynamics is normally used to predict the energy exchanges that occur in the following processes:

  • Chemical reactions
  • phase changes
  • The formation of solutions.

The following state functions are of primary concern in chemical thermodynamics:

  • Internal energy (U)
  • Enthalpy (h). Enthalpy is a physical quantity defined in the field of classical thermodynamics to measure the maximum energy of a thermodynamic system theoretically capable of being removed from it in the form of heat. It is particularly useful to understand and describe isobaric processes: constant pressure, enthalpy variation is directly associated with the energy received by the system in the form of heat, these are easily quantifiable with calorimeters.
  • Entropy (S). Entropy is a thermodynamic magnitude that explains the energy that cannot be performed by useful work in a thermodynamic process. It is a function of an extended character state and its value increases in an isolated system, according to the second law of thermodynamics. It can be interpreted as the state of disorder of a system. The positive entropy change indicates the natural sense in which any event occurs in an isolated system.
  • Gibbs free energy (G). In thermodynamics, Gibbs free energy (or free enthalpy) is a mathematical expression, more specifically an extended state function, that provides the condition of equilibrium and spontaneity for any process that takes place under constant pressure (for example, many reactions) . chemical products). Changes in free energy are symbolized as ΔG and represent the energy available for useful chemical work.

Most identities in chemical thermodynamics arise from the application of the first law of thermodynamics and the second law of thermodynamics, in particular the law of conservation of energy, to these state functions.

Laws of Thermodynamics

In summary, the three laws of thermodynamics announce the following:

The energy of the universe is constant.
In any spontaneous process, there is always an increase in the entropy of the universe.
The entropy of a perfect (well-ordered) crystal at 0 Kelvin is zero.

The laws of thermodynamics describe, in principle, the private transport of heat and work in thermodynamic processes. However, since their conception, these laws of physics became the most important in all Physics and other sciences related to thermodynamics. They are often associated with concepts that are too far removed from what their statements contain.

Laws of thermodynamics

0. zeroth law of thermodynamics.

1. first law of thermodynamics.

2. second law of thermodynamics.

3. third law of thermodynamics.

The first principle to be established was the second law of thermodynamics, as formulated by Sadi Carnot in 1824. In 1860 he already established two "principles" of thermodynamics with the works of Rudolf Clausius and William Thomson, Lord Kelvin. Over time, these principles have become "laws." In 1873, for example, Willard Gibbs claimed that there were two absolute laws of thermodynamics in his graphical methods in fluid thermodynamics. A total of four laws are currently enunciated. In the last 80 years, some authors have suggested other laws, but none of them were accepted unanimously.

History of Chemical Thermodynamics

The development of chemical thermodynamics developed simultaneously in two ways: thermochemistry and thermodynamics.

The emergence of thermochemistry as an independent science should be considered as the discovery by Herman Ivanovich Hess, a professor at the University of Petersburg, the relationship between the thermal effects of chemical reactions, Hess's laws.

In 1867, on the basis of thermochemistry, Marselen Berthelot proposed one of the first theories of chemical affinity, explaining the flow direction of chemical reactions.

The general achievements of thermodynamics, as a part of theoretical chemistry, reflected in the study of entropy, led to the emergence of another method of investigation, not related to the negatively proven theory of chemical affinity.

The foundations of classical chemical thermodynamics were laid in Josiah Willard Gibbs's work "On the Equilibrium of Heterogeneous Substances" (1878), in which a graphical method of representing the states of a substance, the method of thermodynamic potentials, was developed. and the phase rule.

Gibbs methods, also developed by Pierre Dueme, gave a great impetus to the development of thermodynamic applications, since they were much simpler than the method of circular processes, which required inventing hypothetical processes that closed a certain process in a circular one.

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Published: October 30, 2018
Last review: October 30, 2018