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Chemical Thermodynamics

Chemical Thermodynamics

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

Chemical thermodynamics involve not only laboratory measurements of various thermodynamic properties, but also the application of mathematical methods for the study of chemical questions and the spontaneity of processes.

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

History of chemical thermodynamics

In 1865, the German physicist Rudolf Clausius, in his Mechanical Theory of Heat, suggested that the principles of thermochemistry, for example, the heat generated in combustion reactions, could be applied to the principles of thermodynamics. On the basis of Clausius's work, between the years 1873-76 the American mathematical physicist Willard Gibbs published a series of three articles, the most famous was the document On the balance of heterogeneous substances.

In these articles, Gibbs showed how the first two laws of thermodynamics could be measured graphically and mathematically to determine both the thermodynamic equilibrium of chemical reactions and their tendencies to occur or advance. The Gibbs document collection provided the first unified body of thermodynamic theorems based on principles developed by others, such as Clausius and Sadi Carnot.

At the beginning of the twentieth century, two important publications successfully applied the principles developed by Gibbs to chemical processes, and thus laid the foundations of the science of chemical thermodynamics. The first was the 1923 textbook Thermodynamics and the Free Energy of Chemical Substances by Gilbert N. Lewis and Merle Randall. This book was responsible for supplanting the chemical affinity with the term free energy in the English-speaking world.

The second was the 1933 Modern Thermodynamics book by the methods of Willard Gibbs, written by EA Guggenheim .. In this way, Lewis, Randall and Guggenheim are considered the founders of modern chemical thermodynamics due to the great contribution of these two books to unify the application of thermodynamics to chemistry.

Characteristics of chemical thermodynamics

The primary objective of chemical thermodynamics is the establishment of a criterion for the determination of the feasibility or spontaneity of a given transformation.


In this way, chemical thermodynamics is generally 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 paramount importance in chemical thermodynamics:

  • The internal energy (U).
  • Enthalpy (H).
  • Entropy (S).
  • The free energy of Gibbs (G).

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

The 3 laws of thermodynamics:

  • First law of thermodynamics: The energy of the universe is constant.
  • Second law of thermodynamics: In any spontaneous process, there is always an increase in the entropy of the universe
  • Third law of thermodynamics: The entropy of a perfect crystal (well ordered) at 0 Kelvin is zero
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Last review: February 21, 2018