Chemistry
Entropy Change
Entropy change refers to the measure of the disorder or randomness in a system during a chemical reaction or physical process. It is denoted by the symbol ΔS and can be positive or negative, indicating an increase or decrease in disorder, respectively. Entropy change is a key concept in understanding the spontaneity and direction of chemical reactions.
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12 Key excerpts on "Entropy Change"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
Energy dispersal The concept of entropy can be described qualitatively as a measure of energy dispersal at a specific temperature. Similar terms have been in use from early in the history of classical thermodynamics, and with the development of statistical thermodynamics and quantum theory, Entropy Changes have been described in terms of the mixing or spreading of the total energy of each constituent of a system over its particular quantized energy levels. Ambiguities in the terms disorder and chaos , which usually have meanings directly opposed to equilibrium, contribute to widespread confusion and hamper comprehension of entropy for most students. As the second law of thermodynamics shows, in an isolated system internal portions at different temperatures will tend to adjust to a single uniform temperature and thus produce equilibrium. A recently developed educational approach ________________________ WORLD TECHNOLOGIES ________________________ avoids ambiguous terms and describes such spreading out of energy as dispersal, which leads to loss of the differentials required for work even though the total energy remains constant in accordance with the first law of thermodynamics (compare discussion in next section). Physical chemist Peter Atkins, for example, who previously wrote of dispersal leading to a disordered state, now writes that spontaneous changes are always accompanied by a dispersal of energy. Relating entropy to energy usefulness Following on from the above, it is possible (in a thermal context) to regard entropy as an indicator or measure of the effectiveness or usefulness of a particular quantity of energy. This is because energy supplied at a high temperature (i.e. with low entropy) tends to be more useful than the same amount of energy available at room temperature. Mixing a hot parcel of a fluid with a cold one produces a parcel of intermediate temperature, in which the overall increase in entropy represents a “loss” which can never be replaced.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
Energy dispersal The concept of entropy can be described qualitatively as a measure of energy dispersal at a specific temperature. Similar terms have been in use from early in the history of classical thermodynamics, and with the development of statistical thermodynamics and quantum theory, Entropy Changes have been described in terms of the mixing or spreading of the total energy of each constituent of a system over its particular quantized energy levels. Ambiguities in the terms disorder and chaos , which usually have meanings directly opposed to equilibrium, contribute to widespread confusion and hamper comprehension of entropy for most students. As the second law of thermodynamics shows, in an isolated system internal portions at different temperatures will tend to adjust to a single uniform temperature and thus produce equilibrium. A recently developed educational approach avoids ambiguous terms and describes such spreading out of energy as dispersal, which leads to loss of the differentials required for work even though the total energy remains constant in accordance with the first law of thermodynamics (compare discussion in next section). Physical chemist Peter Atkins, for example, who previously wrote of dispersal leading to a disordered state, now writes that spontaneous changes are always accompanied by a dispersal of energy. ________________________ WORLD TECHNOLOGIES ________________________ Relating entropy to energy usefulness Following on from the above, it is possible (in a thermal context) to regard entropy as an indicator or measure of the effectiveness or usefulness of a particular quantity of energy. This is because energy supplied at a high temperature (i.e. with low entropy) tends to be more useful than the same amount of energy available at room temperature. Mixing a hot parcel of a fluid with a cold one produces a parcel of intermediate temperature, in which the overall increase in entropy represents a “loss” which can never be replaced.
eBook - PDFChemistry
Structure and Dynamics
- James N. Spencer, George M. Bodner, Lyman H. Rickard(Authors)
- 2011(Publication Date)
- Wiley(Publisher)
In some cases, such as the melting of a solid or the breaking apart of a larger molecule into smaller molecules, an increase in disorder can be readily inferred. Because entropy is a state function, the change in entropy that occurs as a system is transformed from some initial state to some final state can be calculated as follows. When a process produces an increase in the disorder of the universe, the Entropy Change, ¢S univ , is positive. 13.3 Entropy and the Second Law of Thermodynamics As noted in Section 7.1, thermodynamics is the study of energy and its transfor- mations. The first law of thermodynamics, discussed in Chapter 7, provides us with ways of understanding energy changes in chemical reactions. The second law of thermodynamics helps us determine the direction in which natural processes such as chemical reactions should occur. The role that disorder plays in determining the direction in which a natural process occurs is summarized by the second law, which states that for a process to occur, the entropy of the universe must increase. The term universe means everything that might conceivably have its entropy altered as a result of the process. The second law of thermodynamics can therefore be written as follows. This statement means that processes for which ¢S univ 7 0 will occur naturally, but that processes for which ¢S univ 6 0 will probably never occur. If ¢S univ 0, the process may occur in either direction. It is important to recognize that the second law of thermodynamics describes what happens to the entropy of the universe, not the system. The universe is divided into two components, the system and its surroundings. The change in the entropy of the universe is the sum of the change in the entropy of the system and the surroundings. Chemists generally choose the chemical reaction in which they are interested as the system. The term surroundings is then used to describe the environment that is altered as a consequence of the reaction.
eBook - ePub- Patrick E. McMahon, Rosemary McMahon, Bohdan Khomtchouk(Authors)
- 2019(Publication Date)
- CRC Press(Publisher)
25 ThermodynamicsEntropy and Free EnergyI GENERAL CONCEPTS OF ENTROPY The entropy of a system (symbol = S(system) ) is a measure of the disorder, or randomness, of that system. The larger the entropy value the greater the randomness, or disorder, of the system; the smaller the entropy value, the lesser the randomness or disorder (or, equivalently, the smaller the entropy value, the more ordered the system).Entropy measures the statistical probabilities of specific system configurations vs. all possible configurations (termed the degrees of freedom).Randomness, or disorder, always represents the more probable arrangement of matter. The result is that entropy always increases in the direction of increasing probability of the arrangement of matter within a system.Entropy is a state function, the change in entropy of any system depends only on the initial and final states and not on how the change occurs. Randomness, or disorder, in a system of matter is related to the number of arrangements in which the matter can exist. General trends for a specific amount of matter are:(1)
No longer available |Learn more- (Author)
- 2014(Publication Date)
- White Word Publications(Publisher)
Energy dispersal The concept of entropy can be described qualitatively as a measure of energy dispersal at a specific temperature. Similar terms have been in use from early in the history of classical thermodynamics, and with the development of statistical thermodynamics and quantum theory, Entropy Changes have been described in terms of the mixing or spreading of the total energy of each constituent of a system over its particular quantized energy levels. Ambiguities in the terms disorder and chaos , which usually have meanings directly opposed to equilibrium, contribute to widespread confusion and hamper comprehension of entropy for most students. As the second law of thermodynamics shows, in an isolated system internal portions at different temperatures will tend to adjust to a single uniform temperature and thus produce equilibrium. A recently developed educational approach avoids ambiguous terms and describes such spreading out of energy as dispersal, which leads to loss of the differentials required for work even though the total energy remains constant in accordance with the first law of thermodynamics (compare discussion in next section). Physical chemist Peter Atkins, for example, who previously wrote of dispersal leading to a disordered state, now writes that spontaneous changes are always accompanied by a dispersal of energy. Relating entropy to energy usefulness Following on from the above, it is possible (in a thermal context) to regard entropy as an indicator or measure of the effectiveness or usefulness of a particular quantity of energy. This is because energy supplied at a high temperature (i.e. with low entropy) tends to be more useful than the same amount of energy available at room temperature. Mixing a hot parcel of a fluid with a cold one produces a parcel of intermediate temperature, in which the overall increase in entropy represents a “loss” which can never be replaced.
eBook - PDF- Young, William Vining, Roberta Day, Beatrice Botch(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
In all cases, Interactive Figure 20.1.1 Explore directionality in chemical processes. 1 2 3 Hydrogen balloon explosion sequence Charles D. Winters Figure 20.1.2 A nonspontaneous process: splitting water into hydrogen and oxygen Charles D. Winters Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 Unit 20 Thermodynamics: Entropy and Free Energy 634 these terms refer to the random molecular energy within a system in the form of trans-lational, rotational, and vibrational motion of the particles. Increasing the temperature increases the random motion of the particles within a substance and, thus, increases its entropy. Spontaneous change always occurs in the direction of increasing total entropy. An iso-lated system, one that cannot exchange matter or energy with the surroundings (imagine a thermos bottle), will never spontaneously decrease in entropy. It will remain unchanged or move to higher entropy. Therefore, Entropy Change is about the dispersal of energy, in the form of matter or thermal energy, as shown in Interactive Figure 20.1.3. Here are some statements of the second law using the concept of entropy: ● All physical and chemical changes occur such that the total entropy of the universe increases. uni2206 S universe 5 uni2206 S system 1 uni2206 S surroundings 7 0 for a spontaneous process (20.1) ● The entropy of an isolated system never spontaneously decreases. uni2206 S isolated $ 0 Note that the entropy of a system could go down, provided that the entropy of the sur-roundings goes up more, or visa versa, so that the sum of the changes is greater than zero. The underlying message is that for an exchange of energy to occur spontaneously, some of the energy must become more diffuse. The consequence is that some energy must always be discarded as heat. Other ways to say this include: ● It is impossible to completely turn heat (diffuse energy) into work (concentrated energy).
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
Ambiguities in the terms disorder and chaos , which usually have meanings directly opposed to equilibrium, contribute to widespread confusion and hamper comprehension of entropy for most students. As the second law of thermodynamics shows, in an isolated system internal portions at different temperatures will tend to adjust to a single uniform temperature and thus produce equilibrium. A recently developed educational approach avoids ambiguous terms and describes such spreading out of energy as dispersal, which leads to loss of the differentials required for work even though the total energy remains constant in accordance with the first law of ______________________________ WORLD TECHNOLOGIES ______________________________ thermodynamics (compare discussion in next section). Physical chemist Peter Atkins, for example, who previously wrote of dispersal leading to a disordered state, now writes that spontaneous changes are always accompanied by a dispersal of energy. Relating entropy to energy usefulness Following on from the above, it is possible (in a thermal context) to regard entropy as an indicator or measure of the effectiveness or usefulness of a particular quantity of energy. This is because energy supplied at a high temperature (i.e. with low entropy) tends to be more useful than the same amount of energy available at room temperature. Mixing a hot parcel of a fluid with a cold one produces a parcel of intermediate temperature, in which the overall increase in entropy represents a “loss” which can never be replaced. Thus, the fact that the entropy of the universe is steadily increasing, means that its total energy is becoming less useful: eventually, this will lead to the heat death of the Universe. Ice melting example The illustration here is a classic example in which entropy increases in a small universe, a thermodynamic system consisting of the surroundings (the warm room) and system (glass, ice, cold water).
eBook - PDF- Lokesh Pandey(Author)
- 2020(Publication Date)
- Arcler Press(Publisher)
This can be understood as the distribution of the thermal energy among the thermal microparticles that may be moving randomly in space. The entropy can be considered as the measure of the thermal energy in its random and redistributed form which has been integrated over a certain range of temperature. The redistribution may have taken due to the transfer of heat or a heat generation which is irreversible in nature and has taken place due to the degradation of energy. The generation of heat may have more than one aspect to look forward to and may be elusive in nature. This redistribution may take place within a structure of material system in space as per the absolute temperature level and may be given by: dS = dQ sys /T = m C sys dT/T The unit of this may be J/K. The entropy of a system may also be given as the measure of the thermal disorder which is given in relation to the logarithm of the number of all the thermal and dynamic microstates, given by W, which is based on the position and the moment of the microparticles and expressed as S = k B ln W Some people like to introduce the concept of entropy as the measure of the disorder or the randomness and state that the destruction of entropy is brought about when some order is created, giving the example of the manner in which life evolved. However, it may be noted that at the time of any of the processes, which may be natural or man-made and which may be of creating or destroying any order or disorder, that is the transformation of any structure of material, the work potential may be regarded as always being dissipated into heat and in such a case the generation of entropy will always be there.
eBook - PDF- John A. Olmsted, Gregory M. Williams, Robert C. Burk(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
557 CHAPTER 12 Spontaneity of Chemical Processes LEARNING OBJECTIVES Upon completion of this chapter you should be able to: • recognize the driving force behind all chemical change: dispersal of energy and matter • predict the direction of change based on the Entropy Changes in the system and in the surroundings • understand and calculate entropies of pure substances • predict the direction of spontaneous change using the reaction free energy • apply thermodynamics to chemical reactions and phase changes • describe thermodynamically some representative energetic processes that operate in living organisms CHAPTER CONTENTS 12.1 Spontaneity 12.2 Entropy: The Measure of Dispersal 12.3 Entropies of Pure Substances 12.4 Spontaneity and Free Energy 12.5 Some Applications of Thermodynamics 12.6 Bioenergetics NASA's Goddard Space Flight Center 100 nm Dr. Anatoli Ianoul, Carleton University 558 CH A P TER 12 Spontaneity of Chemical Processes 12.1 Spontaneity Every process has a preferred direction, which is referred to in thermodynamics as the spontaneous direction. Left to itself, a process follows its spontaneous direction. For exam- ple, the spontaneous direction for water movement is downhill, from higher altitude to lower altitude. A spontaneous process can be reversed only by the action of some outside force. Water runs uphill only if an external agent, such as a pump, forces it to do so. A process may be spontaneous, and yet the process may not occur. Extending our water example, water can be stored behind a dam for a very long time unless a spillway is opened. A chemical example is the reaction of methane and oxygen to form carbon dioxide and water: CH 4 ( g) + 2 O 2 ( g) ⟶ CO 2 ( g) + 2 H 2 O(l ) Spontaneous direction Methane–oxygen mixtures can be stored indefinitely, but a spark will cause the mixture to burst into flames. A process that does not appear to occur may be spontaneous but very slow, or it may be non-spontaneous.
eBook - PDFChemistry
An Atoms First Approach
- Steven Zumdahl, Susan Zumdahl, Donald J. DeCoste, , Steven Zumdahl, Steven Zumdahl, Susan Zumdahl, Donald J. DeCoste(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
You throw these cards into the air and pick them all up at random. Looking at the new sequence of the cards, you would be very surprised to find that it matched the original order. Such an event would be possible, but very improbable. There are billions of ways for the deck to be disordered, but only one way to be or- dered according to your definition. Thus the chances of picking the cards up out of order are much greater than the chance of picking them up in order. It is natural for disorder to increase. Entropy is a thermodynamic function that describes the number of arrangements (positions and/or energy levels) that are available to a system existing in a given state. Entropy is closely associated with probability. The key concept is that the more ways a particular state can be achieved, the greater is the likelihood (probability) of finding that state. In other words, nature spontaneously proceeds toward the states that have the highest probabilities of existing. This conclusion is not surprising at all. The difficulty comes in connecting this concept to real-life processes. For example, what does the spontaneous rusting of steel have to do with probability? Understand- ing the connection between entropy and spontaneity will allow us to answer such questions. We will begin to explore this connection by considering a very simple process, the expansion of an ideal gas into a vacuum, as represented in Fig. 16.3. Why is this process spontaneous? The driving force is probability. Because there are more ways of having the gas evenly spread throughout the container than there are ways for it to be in any other possible state, the gas spontaneously attains the uni- form distribution. To understand this conclusion, we will greatly simplify the system and consider the possible arrangements of only four gas molecules in the two-bulbed container (Fig. 16.4).
eBook - PDFPhysical Principles of Chemical Engineering
International Series of Monographs in Chemical Engineering
- Peter Grassmann, H. Sawistowski(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
The people do not sit still there, they tend to move now forwards, now backwards, even occasionally two people side by side may exchange places with each other—this is also found t For quantum-mechanical reasons a zero-point energy may be found even at absolute zero point. This will be ignored in the following, however. 58 Concept and Use of Entropy [§2.1 with atoms where it corresponds to their thermal motion. Also some seats are empty, but, on the whole, the arrangement is fairly complete. This arrange-ment is destroyed, but not completely, when the crystalline body melts. Then we can compare the arrangement and motion of the atoms with people stand-ing in a hall. It is now no longer possible to speak of a fixed array, it is relatively simple to change places, but the distances between the individuals do not vary greatly from a mean distance, so that within small regions we can virtually still talk of a lattice structure. An increase in the entropy generally also corresponds to a rise in tempera-ture, but this need not be the case; at melting and boiling points the entropy, but not the temperature, rises; the heat supplied is used exclusively to destroy the order of the connection between the atoms, while the mean kinetic energy of the atoms, and hence the temperature, remain constant. Typical is the fact that in the case of all liquids the transition from liquid to vapour corresponds to an almost equal increase in the disorder per mole because, according to Trouton's rule, the molar heat of vaporization divided by the absolute tem-perature of the normal boiling point—i.e. the molar entropy of vaporization—is of the same magnitude in the case of all normal liquids. Finally, as we approach the ideal gas, the state of maximum disorder is attained—each molecule is completely independent of the others. The molecules are scattered over the available space and are only subject to the laws of probability. Mostly the increase in entropy is accompanied by an increase in volume. The body expands during heating, the volume of the vapour exceeds that of the liquid, and this in turn exceeds that of the solid body; just as there is ample room in a suitcase when it is packed in an orderly
eBook - ePubThermodynamics Kept Simple - A Molecular Approach
What is the Driving Force in the World of Molecules?
- Roland Kjellander(Author)
- 2015(Publication Date)
- CRC Press(Publisher)
A process is spontaneous provided the total entropy increases. It is important to include all Entropy Changes, so that we really obtain the total Entropy Change. If our system interacts with its surroundings, we must also include the change in the entropy of the surroundings, S surr. It is the total entropy S tot = S system + S surr that increases during a spontaneous process. S system may increase or decrease depending on the circumstances. 44 If we, for example, have a warm system in contact with a cold environment, S system spontaneously decreases as heat flows from the system to the surroundings. S surr, however, will increase more than S system decreases, so the total entropy increases. It is commonly said that the entropy of the “whole universe” increases during spontaneous processes – which we, however, should take with a grain of salt, because we hardly know enough about the universe to say such a thing with certainty. That entropy increases is often popularly described as a decrease in order – a disordered macroscopic state would thus be more probable than an ordered one. This is usually true but not always. There are examples of systems that have higher entropy in an ordered state than in a disordered one. Remember that high entropy corresponds to many different possibilities for the system – many different particle configurations and different energy distributions. An example from everyday life is in order. If we fill a large box with books that we just throw down in a helter-skelter manner, we find that the books lock one another’s positions when the box is full. Their freedom to move around is very limited when we shake the closed box slightly. If we instead pack the box with the same books by neatly arranging the books in the box, we find that there is a rather large empty space left. When we shake the closed box in this case, the books have much more freedom to move
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