'Thermodynamics' (from the
Greek θερμη, ''therme,'' meaning "
heat" and δυναμις, ''dynamis,'' meaning "
power") is a branch of
physics that studies the effects of changes in
temperature,
pressure, and
volume on
physical systems at the
macroscopic scale by analyzing the collective motion of their particles using
statistics.
[ A to Z of Thermodynamics, Perrot, Pierre, , , Oxford University Press, 1998, ISBN 0-19-856552-6 ][1] Roughly,
heat means "energy in transit" and
dynamics relates to "movement"; thus, in essence thermodynamics studies the movement of energy and how energy instills movement. Historically, thermodynamics developed out of need to increase the
efficiency of early
steam engines.
[2]
Typical '
thermodynamic system' - heat moves from hot (boiler) to cold (condenser), (both not shown) and
work is extracted, in this case by a series of pistons.
The starting point for most thermodynamic considerations are the
laws of thermodynamics, which postulate that
energy can be exchanged between physical systems as heat or
work.
[3] They also postulate the existence of a quantity named
entropy, which can be defined for any system.
[4] In thermodynamics, interactions between large ensembles of objects are studied and categorized. Central to this are the concepts of ''
system'' and ''
surroundings''. A system is composed of particles, whose average motions define its properties, which in turn are related to one another through
equations of state. Properties can be combined to express
internal energy and
thermodynamic potentials, which are useful for determining conditions for
equilibrium and
spontaneous processes.
With these tools, thermodynamics describes how systems respond to changes in their surroundings. This can be applied to a wide variety of topics in
science and
engineering, such as
engines,
phase transitions,
chemical reactions,
transport phenomena, and even
black holes. The results of thermodynamics are essential for other fields of
physics and for
chemistry,
chemical engineering,
aerospace engineering,
mechanical engineering,
cell biology,
biomedical engineering, and
materials science to name a few.
[5][6]
History
'
Sadi Carnot' (1796-1832): the "father" of thermodynamics
A brief history of thermodynamics begins with
Otto von Guericke who in 1650 built and designed the world's first
vacuum pump and created the world's first ever
vacuum (known as the
Magdeburg hemispheres). He was driven to make a vacuum in order to disprove
Aristotle's long-held supposition that 'nature abhors a vacuum'. Shortly thereafter, Irish physicist and chemist
Robert Boyle had learned of Guericke's designs and in 1656, in coordination with English scientist
Robert Hooke, built an air pump.
[7] Using this pump, Boyle and Hooke noticed the pressure-temperature-volume correlation. In time, Boyle's Law was formulated, which states that pressure and volume are inversely proportional. Then, in 1679, based on these concepts, an associate of Boyle's named
Denis Papin built a
bone digester, which was a closed vessel with a tightly fitting lid that confined steam until a high pressure was generated.
Later designs implemented a steam release valve that kept the machine from exploding. By watching the valve rhythmically move up and down, Papin conceived of the idea of a piston and a cylinder engine. He did not, however, follow through with his design. Nevertheless, in 1697, based on Papin's designs, engineer
Thomas Savery built the first engine. Although these early engines were crude and inefficient, they attracted the attention of the leading scientists of the time. One such scientist was
Sadi Carnot, the "father of thermodynamics", who in 1824 published ''“Reflections on the Motive Power of Fire”,'' a discourse on heat, power, and engine efficiency. The paper outlined the basic energetic relations between the
Carnot engine, the
Carnot cycle, and
Motive power. This marks the start of thermodynamics as a modern science.
The term ''thermodynamics'' was coined by
James Joule in 1858 to designate the science of relations between
heat and
power.
By
1849, "thermo-dynamics", as a functional term, was used in
William Thomson's paper ''An Account of Carnot's Theory of the Motive Power of Heat.''
[8] The first thermodynamic textbook was written in
1859 by
William Rankine, originally trained as a physicist and a civil and mechanical engineering professor at the
University of Glasgow.
[9]
Classical thermodynamics
Main articles: Classical thermodynamics
'Classical thermodynamics' is the original early 1800s variation of thermodynamics concerned with thermodynamic states, and properties as energy, work, and heat, and with the laws of thermodynamics, all lacking an atomic interpretation. In precursory form, classical thermodynamics derives from chemist
Robert Boyle’s
1662 postulate that the pressure ''P'' of a given quantity of gas varies inversely as its volume ''V'' at constant temperature; i.e. in equation form: ''PV = k'', a constant. From here, a semblance of a thermo-science began to develop with the construction of the first successful atmospheric steam engines in England by
Thomas Savery in 1697 and
Thomas Newcomen in
1712. The first and second laws of thermodynamics emerged simultaneously in the 1850s, primarily out of the works of
William Rankine,
Rudolf Clausius, and
William Thomson (Lord Kelvin).
[10]
Statistical thermodynamics
Main articles: Statistical thermodynamics
With the development of atomic and molecular theories in the late
19th century, thermodynamics was given a molecular interpretation. This field is called 'statistical thermodynamics', which can be thought of as a bridge between macroscopic and microscopic properties of systems.
[11] Essentially, statistical thermodynamics is an approach to thermodynamics situated upon
statistical mechanics, which focuses on the derivation of macroscopic results from first principles. It can be opposed to its historical predecessor
phenomenological thermodynamics, which gives scientific descriptions of phenomena with avoidance of microscopic details. The statistical approach is to derive all macroscopic properties (temperature, volume, pressure, energy, entropy, etc.) from the properties of moving constituent particles and the interactions between them (including quantum phenomena). It was found to be very successful and thus is commonly used.
Chemical thermodynamics
Main articles: Chemical thermodynamics
'Chemical thermodynamics' is the study of the interrelation of
heat with
chemical reactions or with a physical change of
state within the confines of the
laws of thermodynamics. During the years 1873-76 the American mathematical physicist
Josiah Willard Gibbs published a series of three papers, the most famous being ''
On the Equilibrium of Heterogeneous Substances'', in which he showed how
thermodynamic processes could be graphically analyzed, by studying the
energy,
entropy,
volume,
temperature and
pressure of the
thermodynamic system, in such a manner to determine if a process would occur spontaneously.
[12] During the early 20th century, chemists such as
Gilbert N. Lewis,
Merle Randall, and
E. A. Guggenheim began to apply the mathematical methods of Gibbs to the analysis of chemical processes.
[13]
Thermodynamic systems
Main articles: Thermodynamic system
An important concept in thermodynamics is the “system”. Everything in the universe except the system is known as surroundings. A system is the region of the universe under study. A system is separated from the remainder of the universe by a
boundary which may be imaginary or not, but which by convention delimits a finite volume. The possible exchanges of
work,
heat, or
matter between the system and the surroundings take place across this boundary. Boundaries are of four types: fixed, moveable, real, and imaginary.
Basically, the “boundary” is simply an imaginary dotted line drawn around the volume of a something in which there is going to be a change in the
internal energy of that something. Anything that passes across the boundary that effects a change in the internal energy of that something needs to be accounted for in the energy balance equation. That “something” can be the volumetric region surrounding a single atom resonating energy, such as
Max Planck defined in 1900, it can be a body of steam or air in a
steam engine, such as
Sadi Carnot defined in 1824, or it can be the body of a
tropical cyclone, such as
Kerry Emanuel theorized in 1986 in the field of
atmospheric thermodynamics, or it can be a single
nuclide, i.e. a system of
quarks, as some are theorizing presently in
quantum thermodynamics.
For an engine, a fixed boundary means the piston is locked at its position; as such, a constant volume process occurs. In that same engine, a moveable boundary allows the piston to move in and out. For closed systems, boundaries are real while for open system boundaries are often imaginary. There are five dominant classes of systems:
#''Isolated Systems'' – matter and energy may not cross the boundary.
#''Adiabatic Systems'' – heat must not cross the boundary.
#''Diathermic Systems'' - heat may cross boundary.
#''Closed Systems'' – matter may not cross the boundary.
#''Open Systems'' – heat, work, and matter may cross the boundary (often called a
control volume in this case).
As time passes in an isolated system, internal differences in the system tend to even out and pressures and temperatures tend to equalize, as do density differences. A system in which all equalizing processes have gone practically to completion, is considered to be in a
state of
thermodynamic equilibrium.
In thermodynamic equilibrium, a system's properties are, by definition, unchanging in time. Systems in equilibrium are much simpler and easier to understand than systems which are not in equilibrium. Often, when analysing a thermodynamic process, it can be assumed that each intermediate state in the process is at equilibrium. This will also considerably simplify the situation. Thermodynamic processes which develop so slowly as to allow each intermediate step to be an equilibrium state are said to be
reversible processes.
Thermodynamic parameters
Main articles: Conjugate variables (thermodynamics)
The central concept of thermodynamics is that of
energy, the ability to do work. As stipulated by the
first law, the total energy of the system and its surroundings is conserved. It may be transferred into a body by heating, compression, or addition of matter, and extracted from a body either by cooling, expansion, or extraction of matter. For comparison, in
mechanics, energy transfer results from a force which causes displacement, the product of the two being the amount of energy transferred. In a similar way, thermodynamic systems can be thought of as transferring energy as the result of a generalized force causing a generalized displacement, with the product of the two being the amount of energy transferred. These thermodynamic force-displacement pairs are known as
conjugate variables. The most common conjugate thermodynamic variables are pressure-volume (mechanical parameters), temperature-entropy (thermal parameters), and chemical potential-particle number (material parameters)..
Thermodynamic instruments
Main articles: Thermodynamic instruments
There are two types of thermodynamic instruments, the 'meter' and the 'reservoir'. A thermodynamic meter is any device which measures any parameter of a
thermodynamic system. In some cases, the thermodynamic parameter is actually defined in terms of an idealized measuring instrument. For example, the
zeroth law states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. This principle, as noted by
James Maxwell in 1872, asserts that it is possible to measure temperature. An idealized
thermometer is a sample of an ideal gas at constant pressure. From the
ideal gas law ''PV=nRT'', the volume of such a sample can be used as an indicator of temperature; in this manner it defines temperature. Although pressure is defined mechanically, a pressure-measuring device, called a
barometer may also be constructed from a sample of an ideal gas held at a constant temperature. A
calorimeter is a device which is used to measure and define the internal energy of a system.
A thermodynamic reservoir is a system which is so large that it does not appreciably alter its state parameters when brought into contact with the test system. It is used to impose a particular value of a state parameter upon the system. For example, a pressure reservoir is a system at a particular pressure, which imposes that pressure upon any test system that it is mechanically connected to. The earth's atmosphere is often used as a pressure reservoir.
It is important that these two types of instruments are distinct. A meter does not perform its task accurately if it behaves like a reservoir of the state variable it is trying to measure. If, for example, a thermometer, were to act as a temperature reservoir it would alter the temperature of the system being measured, and the reading would be incorrect. Ideal meters have no effect on the state variables of the system they are measuring.
Thermodynamic states
Main articles: Thermodynamic state
When a system is at equilibrium under a given set of conditions, it is said to be in a definite ''state''. The state of the system can be described by a number of
intensive variables and
extensive variables. The properties of the system can be described by an
equation of state which specifies the relationship between these variables. State may be thought of as the instantaneous quantitative description of a system with a set number of variables held constant.
Thermodynamic processes
Main articles: Thermodynamic processes
A 'thermodynamic process' may be defined as the energetic evolution of a thermodynamic system proceeding from an initial state to a final state. Typically, each thermodynamic process is distinguished from other processes, in energetic character, according to what parameters, as temperature, pressure, or volume, etc., are held fixed. Furthermore, it is useful to group these processes into pairs, in which each variable held constant is one member of a
conjugate pair. The seven most common thermodynamic processes are shown below:
#An
isobaric process occurs at constant pressure.
#An
isochoric process, or ''isometric/isovolumetric process'', occurs at constant volume.
#An
isothermal process occurs at a constant temperature.
#An
adiabatic process occurs without loss or gain of heat.
#An
isentropic process (reversible adiabatic process) occurs at a constant entropy.
#An
isenthalpic process occurs at a constant enthalpy. Also known as a
throttling process or
wire drawing.
#A
steady state process occurs without a change in the internal energy of a system.
The laws of thermodynamics
Main articles: Laws of thermodynamics
In thermodynamics, there are four laws of very general validity, and as such they do not depend on the details of the interactions or the systems being studied. Hence, they can be applied to systems about which one knows nothing other than the balance of energy and matter transfer. Examples of this include
Einstein's prediction of
spontaneous emission around the turn of the
20th century and current research into the thermodynamics of
black holes.
The four laws are:
★
Zeroth law of thermodynamics, stating that
thermodynamic equilibrium is an
equivalence relation.
::If two thermodynamic systems are separately in thermal equilibrium with a third, they are also in thermal equilibrium with each other.
★
First law of thermodynamics, about the
conservation of energy
::The change in the
internal energy of a closed
thermodynamic system is equal to the sum of the amount of
heat energy supplied to the system and the
work done on the system.
★
Second law of thermodynamics, about
entropy
::The total entropy of any isolated thermodynamic system tends to increase over time, approaching a maximum value.
★
Third law of thermodynamics, about
absolute zero temperature
::As a system
asymptotically approaches absolute zero of temperature all processes virtually cease and the entropy of the system asymptotically approaches a minimum value; also stated as: "the entropy of all systems and of all states of a system is zero at absolute zero" or equivalently "it is impossible to reach the absolute zero of temperature by any finite number of processes".
::''See also:''
Bose–Einstein condensate and
negative temperature.
Thermodynamic potentials
Main articles: Thermodynamic potentials
As can be derived from the energy balance equation on a thermodynamic system there exist energetic quantities called
thermodynamic potentials, being the quantitative measure of the stored energy in the system. The five most well known potentials are:
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Internal energy
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Helmholtz free energy
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Enthalpy
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Gibbs free energy
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Grand potential
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Potentials are used to measure energy changes in systems as they evolve from an initial state to a final state. The potential used depends on the constraints of the system, such as constant temperature or pressure. Internal energy is the internal energy of the system, enthalpy is the internal energy of the system plus the energy related to pressure-volume work, and Helmholtz and Gibbs energy are the energies available in a system to do useful work when the temperature and volume or the pressure and temperature are fixed, respectively.
Quotes & humor
★ Attributed to
Arnold Sommerfeld:
:
See also
Related branches
Lists and timelines
★
History of thermodynamics
★
List of important publications in thermodynamics
★
List of notable textbooks in statistical mechanics
★
Timeline of thermodynamics, statistical mechanics, and random processes
★
Parmenides' influence on the development of thermodynamics
Other
Wikibooks
★
Engineering Thermodynamics
★
References
1. The Essential Dictionary of Science, Clark, John, O.E., , , Barnes & Noble Books, 2004, ISBN 0-7607-4616-8
2. On the Motive Power of Heat, and on the Laws which can be deduced from it for the Theory of Heat, , Ruldolf, Clausius, Poggendorff's ''Annalen der Physick'', LXXIX (Dover Reprint), 1850, ISBN 0-486-59065-8
3. Understanding Thermodynamics, Van Ness, H.C., , , Dover Publications, Inc., 1969, ISBN 0-486-63277-6
4. Entropy and its Physical Meaning, Dugdale, J.S., , , Taylor and Francis, 1998, ISBN 0-7484-0569-0
5. Introduction to Chemical Engineering Thermodynamics, Smith, J.M., , , McGraw Hill, 2005, ISBN 0-07-310445-0
6. Biological Thermodynamics, Haynie, Donald, T., , , Cambridge University Press, 2001, ISBN 0-521-79549-4
7. A Short History of Chemistry, Partington, J.R., , , Dover, 1989, ISBN 0-486-65977-1
8. Kelvin, William T. (1849) "An Account of Carnot's Theory of the Motive Power of Heat - with Numerical Results Deduced from Regnault's Experiments on Steam." ''Transactions of the Edinburg Royal Society, XVI. January 2.'' Scanned Copy
9. Thermodynamics - An Engineering Approach, Cengel, Yunus A.; Boles, Michael A., , , McGraw-Hill, 2005, ISBN 0-07-310768-9
10. Mechanical Theory of Heat, by Rudolf Clausius, 1850-1865
11. Elements of Statistical Thermodynamics, 2nd Ed., Nash, Leonard K., , , Dover Publications, Inc., 1974, ISBN 0-486-44978-5
12. The Scientific Papers of J. Willard Gibbs, Volume One: Thermodynamics, Gibbs, Willard, , , Ox Bow Press, 1993, ISBN 0-918024-77-3
13. Thermodynamics and the Free Energy of Chemical Substances, Lewis, Gilbert N., , , McGraw-Hill Book Co. Inc., 1923,
Further reading
★
Thermodynamics - An Engineering Approach, Cengel, Yunus A., , , McGraw Hill, 2002,
★
Thermal Physics, Kroemer, Herbert; Kittel, Charles, , , W. H. Freeman Company, 1980,
★
The Refrigerator and the Universe, Goldstein, Martin; Inge, F, , , Harvard University Press, 1993,
★
Concise Thermodynamics: Principles and Applications, Dunning-Davies, Jeremy, , , Horwood Publishing, 1997,
External links
★
Thermodynamics at ''ScienceWorld''
★
History of Thermodynamics
★
Shakespeare & Thermodynamics
★
Biochemistry Thermodynamics
★
180+ Variations of the 5 Laws
★
Thermodynamic Evolution
★
Thermodynamics and Statistical Mechanics
★
Thermodynamics - Britannica, 1911 ed.
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