User talk:Lochnagar

Thermodynamics book recommendation
Hi,

I was looking in the discussion section of the Gibbs free energy page and noticed that you've read a serious amount of textbooks on thermodynamics. At the moment I'm really struggling to conceptually understanding what Gibbs free energy is. I have a couple of chemical thermodynamics textbooks (because I'm studying chemical engineering) but they seem to just define Gibbs without giving a detailed explanation of what it is. So I was wondering if you could recommend a thermo. textbook that gives a seriously detailed description of Gibbs, written in such a way that the simpleton (myself) can understand it.

I have this theory that nothing is beyond anyone, it just needs to be explained in such a way that makes it comprehensible. Is this applicable with thermodynamics or do you think that I'm wasting my time trying to understand it?

Thanks for your time, really appreciate it :)

Lochnagar

Reply
Lochnagar,

Good question. Gibbs free energy is my favorite topic. As to being able to conceptually understand what Gibbs free energy is; essentially, it is a more advanced and accurate replacement for the term “affinity” used by chemists, of olden days, to describe the “force” that caused chemical reactions. The term dates back to at least the time of Albertus Magnus in 1250.

From the 1998 textbook Modern Thermodynamics by Nobelist and chemical engineering professor Ilya Prigogine’s we find: “as motion was explained by the Newtonian concept of force, chemists wanted a similar concept of ‘driving force’ for chemical change? Why do chemical reactions occur, and why do they stop at certain points? Chemists called the ‘force’ that caused chemical reactions affinity, but it lacked a clear definition.

During the entire 18th century, the dominate view in regards to heat and light was that put forward by Isaac Newton, called the “Newtonian hypothesis”, which stated that light and heat are forms of matter attracted or repelled by other forms of matter, with forces analogous to gravitation or to chemical affinity.

In the 19th century, the French chemist Marcellin Berthelot and the Danish chemist Julius Thomsen had attempted to quantify affinity using heats of reaction. In 1875, after quantifying the heats of reaction for a large number of compounds, Berthelot proposed the “principle of maximum work” in which all chemical changes occurring without intervention of outside energy tend toward the production of bodies or of a system of bodies which liberate heat.

In addition to this, in 1780 Antoine Lavoisier and Pierre-Simon Laplace laid the foundations of thermochemistry by showing that the heat evolved in a reaction is equal to the heat absorbed in the reverse reaction. They also investigated the specific heat and latent heat of a number of substances, and amounts of heat evolved in combustion. Similarly, in 1840 Swiss chemist Germain Hess formulated the principle that the evolution of heat in a reaction is the same whether the process is accomplished in one-step or in a number of stages. This known as Hess's law. With the advent of the mechanical theory of heat in the early 19th century, Hess’s law came to be viewed as a consequence of the law of conservation of energy.

Based on these and other ideas, Berthelot and Danish chemist Julius Thomsen, as well as others, considered the heat evolved in the formation of a compound as a measure of the affinity, or the work done by the chemical forces. This view, however, was not entirely correct. In 1847, English physicist James Joule showed that raise the temperature of water by turning a paddle wheel in it, thus showing that heat and mechanical work were equivalent or proportion to each other, i.e. approximately, dW α dQ. This was a precursory form of the first law of thermodynamics.

By 1865, the German physicist Rudolf Clausius had showed that this equivalence principle needed amendment. That is, one can use the heat derived from a combustion reaction in a coal furnace to boil water, and use this heat to vaporize steam, and then use the enhanced high pressure energy of the vaporized steam to push a piston. Thus, we might naively reason that one can entirely convert the initial combustion heat of the chemical reaction into the work of pushing the piston. Clausius showed, however, that we need to take into account the work that the molecules of the working body, i.e. the water molecules in the cylinder, do on each other as they pass or transform from one step of or state of the engine cycle to the next, e.g. from (P1,V1) to (P2,V2). Clausius originally called this the “transformation content” of the body, and than later changed the name to entropy. Thus, the heat used to transform the working body of molecule from one state to the next cannot be used to do external work, e.g. to push the piston. Clausius defined this transformation heat as dQ = TdS.

Hence, in 1882, after the introduction of this argument by Clausius, the German scientist Hermann von Helmholtz stated, in opposition to Berthelot and Thomas’ hypothesis that chemical affinity is a measure of the heat of reaction of chemical reaction as based on the principle of maximal work, that affinity is not the heat evolved in the formation of a compound but rather it is the largest quantity of work which can be gained when the reaction is carried out in a reversible manner, e.g. electrical work in a reversible cell. The maximum work is thus regarded as the diminution of the free, or available, energy of the system (Gibbs free energy G at T = constant, P = constant or Helmholtz free energy F at V = constant, P = constant), whilst the heat evolved is usually a measure of the diminution of the total energy of the system (Internal energy). Thus, G or F is the amount of energy “free” for work under the given conditions.

Up until this point, the general view had been such that: “all chemical reactions drive the system to a state of equilibrium in which the affinities of the reactions vanish”. Over the next 60 years, the term affinity came to be replaced with the term free energy. According to chemistry historian Henry Leicester, the influential 1923 textbook Thermodynamics and the Free Energy of Chemical Reactions by Gilbert N. Lewis and Merle Randall led to the replacement of the term “affinity” by the term “free energy” in much of the English-speaking world.

I hope this helps? As to a good book, one that I'm reading this week is the 1967 textbook Nonequilibrium Thermodynamics in Biophysics published by Harvard University Press. It’s written by A. Katchalsky (Polymer Chemistry Department, Institute of Science Rehoveth, Israel) and Peter R. Curran (Biophysical Laboratory, Harvard Medical School, Boston Massachusetts). I’m about halfway through the book and it is very juicy. All the derivations are built from the ground up so you don’t miss any key pieces and they are easy to follow. It shows how the Gibbs free energy equation, in an expanded form, can be applied to very exotic situations, such as when the transport of a substance into muscle tissue causes a chemical reaction, which then does the work of stretching or contracting a muscle fiber. Very stimulating book! As to good chemical engineering thermodynamics textbooks, Smith, Van Ness and Abbott’s textbook is good as well as Sandler’s textbook. Adios: --Sadi Carnot 02:10, 30 July 2006 (UTC)