Chemistry
The Laws of Thermodynamics
The Laws of Thermodynamics are fundamental principles that govern the behavior of energy and matter in the universe. The first law states that energy cannot be created or destroyed, only transformed from one form to another. The second law describes the concept of entropy, which indicates the direction of spontaneous processes and the tendency of systems to move towards disorder.
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12 Key excerpts on "The Laws of Thermodynamics"
- Nils O. Petersen(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
C H A P T E R 6 The basics of thermodynamics 6.1 SOME BASIC CONCEPTS Thermodynamics refers to the field of chemistry which is concerned with un- derstanding the flow of energy within a system or when a system changes from one state to another. One ultimate purpose of thermodynamics is to predict whether a change will occur spontaneously. The field of thermodynamics is based on three fundamental laws which lead to a set of parameters such as the free energy and the chemical potential, which are key to our understanding of spontaneous change. In contrast to the field of quantum mechanics, the field of thermodynamics is, to a first approximation, not concerned with the detailed structures of the materials, and hence the outcomes become very generally applicable. Our first task is to remind ourselves of some basic concepts of systems and how we describe these. A system is simply that region of space or matter that we are interested in understanding. The surroundings of the system is everything else — in principle, everything else in the universe, but in practice everything else that matters, such as the laboratory in which we study the system. For example, the system could be a gas held in a glass container, with the surroundings being the glass container and everything around it. Similarly, the system could be a solution of molecules in a solvent where the system is the molecules in solution and the surroundings include the solvent, the container and everything around it. We characterize a system by a number of functions (or variables) that tell us something unique about the system. Examples would be the temperature of the system, the pressure of the system, the volume of the system, the mass (or the number of molecules) in the system, and the energy of the system. If the state of the system changes, we expect one or more of these functions to change as well, for example, if the number of molecules in the system changes, 99
- Axel Kleidon(Author)
- 2016(Publication Date)
- Cambridge University Press(Publisher)
3 The first and second law of thermodynamics 3.1 The rules for energy conversions The last chapter described how different Earth system processes are related to different forms of energy and entropy. This formulation in terms of energy sets a basis for making them comparable. The rules for converting one form of energy into another are described by The Laws of Thermodynamics. They ensure the conservation of energy during the conversion process, and set the direction into which these conversions occur. Historically, these laws have grown out of the need to understand and improve the work output of steam engines in the mid-nineteenth century. Since then, their basis has been extended much beyond steam engines to all forms of energy transfer. The purpose of this chapter is to show those aspects of The Laws of Thermodynamics that have the most direct relevance to understand energy conversions by Earth sys- tem processes. The foundations set by the laws then allow us to make quantitative predictions of the direction in which the dynamics take place in Earth systems and set upper limits on energy conversion rates, as described in the following chapter. In total, there are four laws of thermodynamics that are numbered from zero to three. They are summarized in Table 3.1. The zeroth law sets the basis for comparing thermodynamic systems. It estab- lishes the state of thermodynamic equilibrium as a reference state, which is the state of a system in which there is no net transformation or exchange of any physical quantity. The zeroth law formulates that if two systems are in thermodynamic equilibrium with a third system, then the two systems are also in thermodynamic equilibrium. As we will see in the following, the state of thermodynamic equi- librium serves as an important reference point, as it sets the “target” state for the dynamics that take place within a system and the exchanges with other systems.
eBook - PDF- Robert DeHoff(Author)
- 2006(Publication Date)
- CRC Press(Publisher)
The Laws of Thermodynamics have a status in science that is similar to Newton’s laws of motion in mechanics and are similarly subject to potential revision in the light of new information. When it was found in physics that new evidence could only be explained by modifying Newton’s laws with Einstein’s relativistic concepts, the laws of motion were generalized. However, this generalization was in such a form that the new equations simplify to Newton’s laws when the velocity of the system is not a significant fraction of the velocity of light. Newton’s laws were not abandoned; they were expanded to include newly discovered phenomena. Classical mechanics could be viewed as a special case of the new relativistic mechanics. This strategy was necessary because classical mechanics successfully described a great body of scientific observations with plausibility and precision. It is possible that new experimental evidence could require a reformulation of The Laws of Thermodynamics. Up to now this has not been necessary, although the discovery of nuclear energy has had to be accommodated by expanding the framework established in the 19th century. 31 The Laws of Thermodynamics are: 1. There exists a property of the universe, called its energy, which cannot change no matter what processes occur. 2. There exists a property of the universe, called its entropy, which always changes in the same direction no matter what processes occur. 3. There exists a lower limit to the temperature that can be attained by matter, called the absolute zero of temperature, and the entropy of all substances is the same at that temperature. A “zeroth law of thermodynamics” is frequently cited, which acknowledges that a temperature scale exists for all substances in nature and provides an absolute measure of their tendencies to exchange heat.
eBook - PDF- Marc J. Assael, William A. Wakeham, Anthony R. H. Goodwin, Stefan Will, Michael Stamatoudis(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
1 1 Chapter Definitions and the 1 st Law of Thermodynamics 1.1 INTRODUCTION The subjects of thermodynamics, statistical mechanics, kinetic theory, and transport phenomena are almost universal within university courses in physical and biological sciences, and engineering. The intensity with which these topics are studied as well as the balance between them varies considerably by disci-pline. However, to some extent the development and, indeed, ultimate practice of these disciplines requires thermodynamics as a foundation. It is, therefore, rather more than unfortunate that for many studying courses in one or more of these topics thermodynamics present a very great challenge. It is often argued by students that the topics are particularly diffi cult and abstract with a large amount of complicated mathematics and rather few practical examples that arise in everyday life. Probably for this reason surveys of students reveal that most strive simply to learn enough to pass the requisite examination but do not attempt serious understanding. However, our lives use and require energy, its conversion in a variety of forms, and understanding these processes is intimately connected to thermodynamics and transport phenomena; the latter is not the main subject of this work. For example, whether a particular proposed new source of energy or a new product is genuinely renewable and/or carbon neutral depends greatly on a global energy balance, on the processes of its production, and its interaction with the environment. This analysis is necessarily based on The Laws of Thermodynamics, which makes it even more important now for all scientists and engineers to have a full appreciation of these subjects as they seek to grapple with increasingly complex and interconnected problems. This book sets out to provide answers to some of the questions that under-graduate students and new researchers raise about thermodynamics and sta-tistical mechanics.
- Peter V. Hobbs(Author)
- 2000(Publication Date)
- Cambridge University Press(Publisher)
2 Chemical thermodynamics Heat can be released or absorbed during a chemical reaction. This pro-vides a powerful method for studying chemical equilibrium by means of chemical thermodynamics. Thermodynamics is based on a few funda-mental postulates, called the first, second, and third laws of thermo-dynamics. We will discuss these laws first, and then apply them to chemical equilibria. 2.1 The first law of thermodynamics; enthalpy In addition to the macroscopic kinetic and potential energy that a body or system as a whole may possess, it also contains internal energy due to the kinetic and potential energy of its molecules or atoms. Increases in internal kinetic energy in the form of molecular motions are manifested as increases in the temperature of the system, while changes in the poten-tial energy of the molecules are caused by changes in their relative configurations. Let us suppose that a system of unit mass takes in a certain quantity of heat energy q (measured in joules). As a result, the system may do a certain amount of external work w (also measured in joules). The excess energy supplied to the system, over and above the external work done by the system, is q - w. Therefore, if there is no change in the macro-scopic kinetic and potential energy of the system, it follows from the principle of conservation of energy that the internal energy of the system must increase by q -w. That is, q - w = u 2 -Mi (2.1) where u x and u 2 are the internal energies of a unit mass of the system before and after the change. In differential form Eq. (2.1) becomes 17 18 Chemical thermodynamics dq-dw = du (2.2) where dq is the differential increment of heat added to a unit mass of the system, dw the differential increment of work done by a unit mass of the system, and du the differential increment in internal energy of a unit mass of the system. Equations (2.1) and (2.2) are statements of the first law of thermodynamics.
eBook - PDF- H J Kreuzer, Isaac Tamblyn;;;(Authors)
- 2010(Publication Date)
- WSPC(Publisher)
Chapter 3 The Laws of Thermodynamics There are four laws of thermodynamics that have been abstracted and gen-eralized from experimental results. Mathematically speaking they are the axioms and postulates on which the edifice of thermodynamics is erected. Fortunately, these laws are today very intuitive and plausible, although they were far from that at the beginning of thermodynamics. 3.1 Zeroth law: The fundamental relation Frequently the status of a zeroth law is accorded to the statement “ If two systems are separately in equilibrium with a third system, they are in equi-librium with each other ”. Although this is a nontrivial statement, a more important role is played by the fact that a single function, namely the en-tropy (as a function of the extensive variables of a system), controls and defines all its equilibrium properties; it is therefore also called the Fun-damental Relation . We will see shortly that the statement on the equi-librium of three systems can be derived from the first and second law of thermodynamics. For completeness, we recall that S is extensive. This im-plies that S ( λU, λV, λN ) = λS ( U, V, N ), i.e. S is a homogeneous function of first order. Entropy is a measure of disorder in the system. To understand this let us look at an example from everyday life. Example 3.1. Assume we want to place n indistinguishable objects into N compartments, at most one in each. If n = N we just need to make one trial and we know for certain that each compartment houses one object; the disorder is zero. If n 6 = N we have a total of Ω = ( N n ) choices all leading to different sets of compartments being occupied by an object; disorder 37 38 Thermodynamics is large. Because entropy is introduced as a measure of disorder it must be a function of Ω, but which function S = S (Ω) is it? We do another experiment, this time with two sets of compartments A and B into which we can distribute the objects.
eBook - PDFEnergy Conversion Engineering
Towards Low CO2 Power and Fuels
- Ahmed F. Ghoniem(Author)
- 2021(Publication Date)
- Cambridge University Press(Publisher)
2 Thermodynamics 2.1 Introduction 1 Thermodynamics is central to the analysis of energy conversion processes and systems. Although excluding rate processes, equilibrium thermodynamics’ analysis can be used to examine the efficiency and specific work of a process or a series of processes executing work and heat transfer interactions with other systems, experiencing mass transfer, undergoing chemical and electrochemical reactions, or a combination of all of these events. Non- equilibrium and rate processes can indeed impact efficiency, and are necessary to determine the power as well as other performance measures such as size and emissions. Non- equilibrium effects will be examined in later chapters. In this chapter, the basic laws of equilibrium thermodynamics are reviewed, with an emphasis on some of the origins of the different statements, the meaning of the quantities appearing in these laws, the most relevant forms of the laws to be used in analysis of energy conversion, and some conclusions regarding how these systems should be designed. The early coverage is independent of the working fluid, and focuses on the energy conversion process. Pure substance, ideal gases, and mixtures of ideal gases and their equations of state are also mentioned. We start with generalized forms of the First Law for closed and open systems, defining the different forms of energy storage and work transfer, and how they are impacted by heat and work transfer. This is followed by the Second Law, starting with the positivity of entropy generation for an isolated system, and extending to forms applicable to closed and open systems interacting with their environment. The combined form of the First and Second Laws is then used to define the availability, or maximum work during a process in which a system interacts with its environment. The availability equations for closed and open system analysis are then shown, along with the definitions of irreversibility and lost work.
eBook - PDFAn Introduction to Equilibrium Thermodynamics
Pergamon Unified Engineering Series
- Bernard Morrill, Thomas F. Irvine, James P. Hartnett, William F. Hughes(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
1 First Law of Thermodynamics 1-1 THERMODYNAMICS The field of science called thermodynamics concerns itself with the study of energy and the transformation of that energy. Historically, this branch of science arose from the study of heat. The ability to convert heat into mechanical energy served as the driving force in the evolution of thermodynamics. The last three centuries have seen the focal point of interest in thermodynamics pass through a spectrum from heat engines to relativistic thermodynamics. Even after three centuries, it is not possible to say that the science of thermodynamics is complete. This text is intended to serve for a first or introductory course in thermodynamics. The usual introduction to thermodynamics is by way of the classical or macroscopic concepts which follow fairly close to the historical evolution of the subject. By macroscopic, we mean that the system under investigation is large enough to be visible and in the main, such properties of the system as pressure, temperature, and mass, can be measured by laboratory devices. The usual or classical approach to the study of thermodynamics concerns itself with macroscopic observations of thermal properties. The properties observed, however, stem from the complex motions of the constituent particles of a system. To base an introduction to the science of thermodynamics solely on macroscopic observations and concepts of matter admits only a limited point of view. This latter statement does not deny the benefits of the classical approach to the study of thermodynamics. It does, however, allow the use of a statistical concept based upon a microscopic view of a thermodynamic system whenever it is thought that such an approach provides insights to 1 2 First Law of Thermodynamics the student. It will be seen that the expected values of certain statistical properties correspond, and are equal to, some of the macroscopic properties which can be measured directly or indirectly.
eBook - PDF- Don Shillady(Author)
- 2011(Publication Date)
- CRC Press(Publisher)
4 The First Law of Thermodynamics INTRODUCTION In the previous chapter, we sharpened our computational skills and gained an appreciation for the particle model of gases. We now turn our attention to matters of energy and energy fl ow according to The Laws of Thermodynamics. In the Math Review chapter, we showed that energy can fl ow between various forms of kinetic and potential energy but that overall energy is conserved and only the form is changed. Many things can be said about thermodynamics. Mainly, thermodynamics owes more to the steam engine than the steam engine owes to thermodynamics. That means that Watt [1] and other inventors built steam engines and got them to work using raw mechanical reasoning and then thermodynamics was developed = discovered to understand the principles of the engine. We will try to help you gain a foundation of understanding if you will follow along and use pencil and paper to write out some derivations rather than just read the text. It should be understood that while physics majors develop expertise in electromagnetic theory far more than chemistry majors, it is generally true that chemistry majors gain a better understanding of thermodynamics. Chemical engineers use thermodynamics as their main expertise, although augmented by kinetics and transport theory, so the chemistry professionals should take pride that thermodynamics is ‘‘ their thing, ’’ their chance to shine in terms of the scienti fi c method. Thermodynamics is necessarily more abstract than the study of mechanical devices because it is not always easy to see ‘‘ heat. ’’ You will soon see that thermodynamics is wonderful for providing information about ‘‘ after-minus-before ’’ processes, but often it tells us little about the mechanism of the process being considered. The good news is that we do not need to know the details of the mechanism of a process, but the bad news is that often thermodynamics does not provide any means to determine the mechanism.
eBook - PDF- R. Prasad(Author)
- 2016(Publication Date)
- Cambridge University Press(Publisher)
A system may be given energy or energy from a system may be withdrawn by carrying out some operation or process on the system. The first law of thermodynamics deals with such situations. The total energy E total of a system may be written as, E total = U T E E E E external Bulk kinetic Bulk Potential any other ( ) + = + ( ) + form of energy 3.15 Thermodynamics: Definitions and the Zeroth Law 107 Energy is measured in terms of the work and, therefore, the units of energy and work are same. The MKS unit of energy is joule (J). Energy may also be expressed in erg, electron volt (eV), kilo watt hour (kWH), British thermal unit (Btu) and calorie (cal). The conversion factors are given below. 1J = I N m; 1 eV = 1.602 × 10 –19 J; 1 erg = 1 × 10 –7 J; 1 cal = 4.1868 J; 1 Btu = 1.0550 × 10 3 J. 3.4 Equilibrium Equilibrium occupies a central place in thermodynamics. A system is said to be in equilibrium if no change in its state functions occur with time. In principle, therefore, it is required to keep the system in observation for infinite time to ensure that no change in system parameters has taken place. Observation of a system for infinite time is possible only in imagination and in practice if system parameter do not change in reasonable time, it is assumed that the system has attained equilibrium. Equilibriums may be of two kinds: (i) natural equilibrium (ii) forced equilibrium or steady state. 3.4.1 Natural equilibrium or equilibrium Any system left to itself for a sufficiently long time attains equilibrium in a natural way. Several examples of natural equilibrium may be given, like hot tea in a cup left for few hours attains the temperature of the surroundings, reaches the state of equilibrium and remains in it for indefinite time without any further efforts. This type of equilibrium, which does not require any effort or energy to maintain equilibrium once it has been attained, is called natural or simply equilibrium.
eBook - PDF- David Ball(Author)
- 2014(Publication Date)
- Cengage Learning EMEA(Publisher)
Many of them demand a certain condition, like constant pressure, constant volume, or constant temperature. Although this might seem inconvenient, by defining the changes in a system in these ways, we can calculate the change in energy of our system. This is an important goal of thermodynamics. As we will see in the next chapter, it is not the only important goal. The other task in thermodynamics is embodied in the question, “What processes tend to occur by themselves, without any effort (that is, work) on our part?” In other words, what processes are spontaneous ? Nothing about the first law of ther-modynamics helps us answer that question unequivocally. That’s because it can’t. A lot of exploration and experimentation showed that energy is not the only con-cern of thermodynamics. Other concerns are also important, and it turns out that those concerns play major roles in how we view our universe. 2 . 1 3 S U M M A R Y K E Y E Q U A T I O N S w 5 2 p ext D V (work against a constant external pressure) w 5 2 nRT ln V f V i 5 2 nRT ln p i p f (reversible work at constant temperature) q 5 mc D T (heat due to temperature change) D U 5 q 1 w (change in internal energy; one way of writing first law) D U 5 q V (change in internal energy at constant volume) H 5 U 1 pV (definition of enthalpy) D H 5 q p (change in enthalpy at constant pressure) a ' U ' T b V 5 C V (heat capacity at constant volume) D U 5 nC V D T (change in internal energy at constant volume) a ' H ' T b p 5 C p (heat capacity at constant pressure) m JT 5 a ' T ' p b H (Joule-Thomson coefficient) Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience.
eBook - PDF- Alberto Patiño Douce(Author)
- 2011(Publication Date)
- Cambridge University Press(Publisher)
But the direction of a spontaneous change in a crystal that is not an isolated system (which is the common situation in nature) is not necessarily determined by an increase in entropy, but rather by a decrease in the thermodynamic potential appropriate to the constraints on the system. We return to this in Sections 4.8 and 4.9. 206 The Second Law of Thermodynamics 4.7 The Third Law of Thermodynamics 4.7.1 Statement of the Third Law of Thermodynamics There is an additional principle, called the Third Law of Thermodynamics, that is inde- pendent of the First and Second Laws. It is essential in the development of chemical thermodynamics, although much of classical thermodynamics and its applications to heat engines and other engineering processes do not require it. We introduce the Third Law by stating that experimental evidence shows that, as temperature approaches 0 K, heat capacities (C P and C V ) approach zero faster than temperature, i.e.: lim T →0 C P T = 0. (4.65) A few examples are shown in Fig. 4.8. A consequence of (4.65) is that the entropy difference of a substance between 0 K and any other temperature, T, is a finite value. Assuming that heating takes place at constant pressure, and that there are no phase transitions between 0 and T, then dQ = C p dT , and we have: S (T ) − S (0) = T 0 d S = T 0 C P T dT (4.66) with condition (4.65) guaranteeing that the integral does not blow up. An unknown integration constant remains, however, which is the entropy at 0 K. 0 50 100 150 200 250 0 0.1 0.2 0.3 0.4 0.5 T (K) C P / T (JK –2 mol –1 ) K Cl Enstatite MgO Fig. 4.8 Low temperature behaviors of C P /T for an ionic crystal (KCl, data from Berg & Morrison, 1957), a crystalline oxide (MgO, data from Barron et al., 1959) and a crystalline silicate (enstatite, data from Krupka et al., 1985).
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