|MadSci Network: Chemistry|
There are 4 generally accepted Laws of Thermodynamics usually referred to as the Zeroth, First, Second and Third Laws. These Laws are based on long standing, careful, empirical work and are based on macroscopic amounts of matter. They depend on bulk properties of matter mostly because individual atoms or particles cannot be defined precisely and cannot be returned to a previous state with any degree of accuracy. However, the thermodynamic laws do follow exactly from kinetic theory, statistical mechanics and quantum mechanics, all of which take the individual particles into account. Zeroth Law: This law is the foundation of temperature and temperature scales. It states that if system A is in thermal equilibrium with system B and if system B is in thermal equilibrium with system C then system A is also in thermal equilibrium with system C. How is the attainment of equilibrium determined? By measuring properties and ascertaining that they are not changing with time, position, distance from the area of thermal contact etc. It does not necessarily mean chemical equilibrium, just that no chemical reaction is occurring at a sufficient rate to be measurable. For example: a stick of dynamite could well be in thermal equilibrium with the hole it is in until the fuse is lit or a battery could be in thermal equilibrium with the flashlight bulb until the switch is closed and could become so again after it runs down and the light dims out. Systems that are in thermal equilibrium with each other are at the same temperature and this temperature is not dependent on the composition of the systems in thermal equilibrium. This law also is expressed in the development of temperature scales based on the concept of an ideal gas, the Second Law of Thermodynamics and from statistical mechanics and kinetic theory. These temperature scales turn out to be the same and are independent of the material being measured [but do depend on the material or method used for the measurement hence the need for temperature standards]. The First Law was formulated about 1850 based on work by Joule and others demonstrating the equivalence of work and heat. This law is the basis of the Law of Conservation of Total Energy. First, it postulates that there exist STATE FUNCTIONS of a system that are dependent only on the initial and final states of a system and are independent of the path from state 1 to state 2. It also states that for a cyclic process where the initial and final states of a system are the same the change in these state functions is zero. An example of such a function is the internal energy, U. A change in the internal energy is defined as the heat gained by a system minus the work done by a system. Heat and work are not state functions; they are path dependent. For a completely isolated system the total energy is constant. Also for a cyclic process where a system is returned to the initial conditions the change in the energy, or any other state function of the system, is zero. The utility of this Law lies in enabling the calculation of energy changes from measurements of system properties in two different states. The First Law enables the calculation of energy changes but doesn’t calculate total energies. The Second Law of Thermodynamics:[Kelvin 1851, Clausius 1854] The second law has many statements. It basically states that that it is impossible to completely convert a quantity of heat into the equivalent amount of work without causing some other change in the system or the environment. In the operation of a heat engine between two different temperatures some heat is transferred to the lower temperature heat reservoir. The ultimate result will be the attainment of equilibrium and the loss of the ability to do work. Other views of the Second Law use the State Function of Entropy. Entropy is a measurement of the randomness of a system. The more random the system the higher the entropy. Entropy can also be measured from the First Law. For a process occurring at constant temperature[isothermal] such as boiling or freezing of water the entropy change is the heat loss or gain divided by the temperature in Kelvins. The Second Law states that any spontaneous process happens with an increase in the entropy of the system and its environment. Other statements indicate that a system will eventually reach equilibrium, a condition of maximum entropy and minimum energy, in which the system can do no work. For a system at equilibrium the Gibbs Free Energy, a state function combining the internal energy and entropy state functions, equals zero and for a chemical system the chemical concentrations are those that satisfy the equilibrium constant. The Second Law enables the predictions of the direction of a reaction or process from First and Third law measurements. It defines the condition of equilibrium. The Second law does not explicitly enable predictions of the rates of chemical reactions; it won’t tell you when that stick of dynamite will explode but will give a good representation of what will happen if it does. An example of the First and Second Laws in operation is the energy the Earth receives from the Sun and subsequently reradiates to outer space. Since the temperature of the Earth remains constant [we are ignoring global warming, biomass storage, and fossil fuel use for now] the First law tells us that the overall change in the internal energy of the Earth is zero. Yet the Earth has used the Sunlight to grow biomass, power the winds and tides, maintain a reasonable temperature etc. The Second Law explains it. The energy from the Sun [black body temperature ~ 6000K, visible light range] consists of a smaller number of photons which have high average energy and low entropy; the energy emitted by the Earth [black body temperature ~350K, infrared range] consists of a much larger number of photons with a much lower average energy and high entropy. The total energy remains constant but the entropy increases. The increase in entropy is what drives the entire Earth. If the Earth were irradiated with sufficient 350K light only, keeping the energy of the Earth constant, the processes that sunlight drives couldn’t happen and an equilibrium would be attained and things would be very different. The Third Law was stated by Nernst in 1905 that the limit of the entropy change for all reactions approaches zero as the temperature approaches absolute zero [0K]. Max Planck extended this in 1913 and stated the Third Law “The entropy of each pure element or substance in perfect crystalline form is zero at absolute zero.” Both views have withstood experimental testing. The second approach has given some interesting insight into materials that do not approach zero entropy near absolute zero. Two examples are nitrous oxide NNO and water HOH, each of which has a statistical arrangement of molecules in its crystal; the crystals show an entropy of mixing. The utility of the Third Law is that is gives a means of calculating equilibrium constants directly from thermodynamic measurements on the reactants and products of a reaction. Both the Third and the Second Law imply that absolute zero can only be approached as a limit. This also has been true according to experiment. The fourth law does not yet seem to have made its way into the textbooks, however, I have been using older texts. We have located some comments on the internet, some of which make some sense. The fourth law seems to have resulted from attempts to relate the 0-3rd Laws to more complex non- thermodynamic systems. It appears to need much refinement, consolidation or experimental quantification before it reaches the status of the others. The following are links or articles that purport to explain the 4th law. This link discusses entropy and the 1st Law http://dove.net.au/~gerhard/ phys16f.htm This is a long winded brief that relates the Laws to what is happening in the world. It requires much critical thought. The following gives a fourth law which makes sense but is not quantified. Sat, 6 Apr 1996 07:34:30 -0800 (PST) Michael Moore (email@example.com) There has been some desire expressed on this list to minimize further discussion of entropy, which is surprising since Nicolas Georgescu-Roegen proposed so ably that entropy is a fundamental economic value which is not limited to mechanical engineers doing heat transfer equations. I have three comments on the subject. First, I've come to express Sadi Carnot's Second Law and G-R's Fourth Law as follows: The Second Law of Thermodynamics: in every transfer of energy, some energy will become unavailable for future use, thus some energy is wasted. The Fourth Law of Thermodynamics: in every contact of matter with matter, some matter will become unavailable for future use, thus some matter is wasted. "Some" is not to imply "minute". Yet the waste of energy is always measureable, while the waste of matter is not. Just to reemphasize, waste means an irrevocable transfer, which is beyond recycling. My formulation can put in perspective the US government's encouragement to increase entropy (waste) by giving allowances in the tax code for depreciation and depletion. We would have a substantially different environmental situation if these allowances were removed. For all the complaint's by business toward waste in government, I've not heard any derision of this encouragement of waste in business. Come to think of it, perhaps we need to reverse the practice by taxing depreciation and depletion, such as consumer goods whose half life is the trip home. My second comment about entropy concerns "closed system". The usual formulation about entropy reminds us that in a "closed system" all events tend toward an equilibrium. The comment was that the universe is a closed system, which I agree. However, our practical reality is the planet earth, which is not a closed system. It receives substantial daily energy from the sun in the form of heat and light. I expect it loses daily energy to "space".[comment it does, vide supra] Thus, thirdly, the entropy factor of our economic formula is small when the economy is deliberately living within the daily budget of the sun's energy. And carefully minimizing waste. The entropy factor is large when the economy exceeds the daily budget by living on yesterday's savings. (Ours is not the first expression of life to create ghost towns.) We only increase our peril when we ignore the entropy factor, we magnify our peril when we discount the entropy factor. G-R points out that all of life converts low entropy to high entropy. Thus our economic task, following the lead of mechanical engineers, is to minimize high entropy of energy and matter which is waste. Respectfully, Michael Moore Poulsbo, Washington, USA This one ?? I do not understand what they are trying to prove. Self-organization: The fourth law of thermodynamics? Charles Curtin and Drew Kerkhoff Ecological Complexity Seminar: Fall 1996 Department of Biology University of New Mexico Outline 1. Criteria for evaluating theoretical constructs 2. Energy dissipation vs. Maximum power 3. Related and required readings Criteria for evaluating theoretical constructs The following criteria for evaluating a new theoretical construct in ecology are suggested by O'Neill et al. (1986): 1. The theory must be internally consistent. 2. The theory must not be adopted simply because of success in other fields. 3. The theory must agree with known properties of ecosystems. 4. The theory must be capable of producing new and testable hypotheses. We present these criteria as a basis for the evaluation of "complexity theory" as we have come to understand it over the course of our discussions and as a starting point for the further self-organization of this seminar. It may be fairly stated that self-organization lies at the basis of complexity as we have come to interpret it. It is the self- organized order of Benard cells that renders the system complex. Below the critical temperature the system exhibits only uniform conduction. The system becomes more interesting when self-organization occurs, and self- organization requires that a system be away from thermodynamic equilibrium. Morowitz (1992) provides an intuitive explanation. Indeed, there is a statement, sometimes called the fourth law of thermodynamics, which states that the flow of energy from a source to a sink through an intermediate system orders that system. Here the word order must be taken as increased complexity. Per Bak (1994) extends this notion of the fourth law, suggesting "that slowly driven systems ... naturally self-organize into a critical state." This implies that in nonequilibrium systems, criticality and complexity may be the rule rather than the exception (Bak 1994). O'Neill et al. (1986) anticipate Bak's conclusion with their proposal that the hierarchical structure of ecosystems is a consequence of the fourth law driving the evolution of increasingly complex nonequilibrium systems from the prebiotic, molecular level to the level of the ecosystem. O'Neill et al. (1986) present the above criteria as a challenge to their notion of hierarchical structure in ecosystems, but perhaps they can be even more usefully applied to the construct that underlies the proposed origin of such structure, the self-organization of nonequilibrium systems, the "fourth law" of thermodynamics. O'Neill, R.V., D.L. DeAngelis, J.B. Waide, and T.F.H. Allen. 1986. Hierarchical structure as the consequence of evolution in open, dissipative systems. in (same authors) A Hierarchical Concept of Ecosystems. Princeton University Press, USA. The thermodynamic Laws are explained at varying levels of understandability in many physical chemistry texts. I recommend Robert A. Alberty Physical Chemistry , Wiley and recommend reading several perhaps starting with the College Outline Series.
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