Econstudentlog

The Laws of Thermodynamics

Here’s a relevant 60 symbols video with Mike Merrifield. Below a few observations from the book, and some links.

“Among the hundreds of laws that describe the universe, there lurks a mighty handful. These are the laws of thermodynamics, which summarize the properties of energy and its transformation from one form to another. […] The mighty handful consists of four laws, with the numbering starting inconveniently at zero and ending at three. The first two laws (the ‘zeroth’ and the ‘first’) introduce two familiar but nevertheless enigmatic properties, the temperature and the energy. The third of the four (the ‘second law’) introduces what many take to be an even more elusive property, the entropy […] The second law is one of the all-time great laws of science […]. The fourth of the laws (the ‘third law’) has a more technical role, but rounds out the structure of the subject and both enables and foils its applications.”

Classical thermodynamics is the part of thermodynamics that emerged during the nineteenth century before everyone was fully convinced about the reality of atoms, and concerns relationships between bulk properties. You can do classical thermodynamics even if you don’t believe in atoms. Towards the end of the nineteenth century, when most scientists accepted that atoms were real and not just an accounting device, there emerged the version of thermodynamics called statistical thermodynamics, which sought to account for the bulk properties of matter in terms of its constituent atoms. The ‘statistical’ part of the name comes from the fact that in the discussion of bulk properties we don’t need to think about the behaviour of individual atoms but we do need to think about the average behaviour of myriad atoms. […] In short, whereas dynamics deals with the behaviour of individual bodies, thermodynamics deals with the average behaviour of vast numbers of them.”

“In everyday language, heat is both a noun and a verb. Heat flows; we heat. In thermodynamics heat is not an entity or even a form of energy: heat is a mode of transfer of energy. It is not a form of energy, or a fluid of some kind, or anything of any kind. Heat is the transfer of energy by virtue of a temperature difference. Heat is the name of a process, not the name of an entity.”

“The supply of 1J of energy as heat to 1 g of water results in an increase in temperature of about 0.2°C. Substances with a high heat capacity (water is an example) require a larger amount of heat to bring about a given rise in temperature than those with a small heat capacity (air is an example). In formal thermodynamics, the conditions under which heating takes place must be specified. For instance, if the heating takes place under conditions of constant pressure with the sample free to expand, then some of the energy supplied as heat goes into expanding the sample and therefore to doing work. Less energy remains in the sample, so its temperature rises less than when it is constrained to have a constant volume, and therefore we report that its heat capacity is higher. The difference between heat capacities of a system at constant volume and at constant pressure is of most practical significance for gases, which undergo large changes in volume as they are heated in vessels that are able to expand.”

“Heat capacities vary with temperature. An important experimental observation […] is that the heat capacity of every substance falls to zero when the temperature is reduced towards absolute zero (T = 0). A very small heat capacity implies that even a tiny transfer of heat to a system results in a significant rise in temperature, which is one of the problems associated with achieving very low temperatures when even a small leakage of heat into a sample can have a serious effect on the temperature”.

“A crude restatement of Clausius’s statement is that refrigerators don’t work unless you turn them on.”

“The Gibbs energy is of the greatest importance in chemistry and in the field of bioenergetics, the study of energy utilization in biology. Most processes in chemistry and biology occur at constant temperature and pressure, and so to decide whether they are spontaneous and able to produce non-expansion work we need to consider the Gibbs energy. […] Our bodies live off Gibbs energy. Many of the processes that constitute life are non-spontaneous reactions, which is why we decompose and putrefy when we die and these life-sustaining reactions no longer continue. […] In biology a very important ‘heavy weight’ reaction involves the molecule adenosine triphosphate (ATP). […] When a terminal phosphate group is snipped off by reaction with water […], to form adenosine diphosphate (ADP), there is a substantial decrease in Gibbs energy, arising in part from the increase in entropy when the group is liberated from the chain. Enzymes in the body make use of this change in Gibbs energy […] to bring about the linking of amino acids, and gradually build a protein molecule. It takes the effort of about three ATP molecules to link two amino acids together, so the construction of a typical protein of about 150 amino acid groups needs the energy released by about 450 ATP molecules. […] The ADP molecules, the husks of dead ATP molecules, are too valuable just to discard. They are converted back into ATP molecules by coupling to reactions that release even more Gibbs energy […] and which reattach a phosphate group to each one. These heavy-weight reactions are the reactions of metabolism of the food that we need to ingest regularly.”

Links of interest below – the stuff covered in the links is the sort of stuff covered in this book:

Laws of thermodynamics (article includes links to many other articles of interest, including links to each of the laws mentioned above).
System concepts.
Intensive and extensive properties.
Mechanical equilibrium.
Thermal equilibrium.
Diathermal wall.
Thermodynamic temperature.
Thermodynamic beta.
Ludwig Boltzmann.
Boltzmann constant.
Maxwell–Boltzmann distribution.
Conservation of energy.
Work (physics).
Internal energy.
Heat (physics).
Microscopic view of heat.
Reversible process (thermodynamics).
Carnot’s theorem.
Enthalpy.
Fluctuation-dissipation theorem.
Noether’s theorem.
Entropy.
Thermal efficiency.
Rudolf Clausius.
Spontaneous process.
Residual entropy.
Heat engine.
Coefficient of performance.
Helmholtz free energy.
Gibbs free energy.
Phase transition.
Chemical equilibrium.
Superconductivity.
Superfluidity.
Absolute zero.

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February 5, 2017 - Posted by | books, Physics

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