Physics
First Law of Thermodynamics
The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another. It is a fundamental principle in physics that governs the conservation of energy within a system. This law is often expressed as the principle of conservation of energy and has wide-ranging applications in various fields of science and engineering.
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11 Key excerpts on "First Law of Thermodynamics"
- Axel Kleidon(Author)
- 2016(Publication Date)
- Cambridge University Press(Publisher)
At the end of the chapter, the key elements are summarized and set in the context of energy conversions within the Earth system. 3.2 The First Law of Thermodynamics In classical thermodynamics, the first law is formulated in terms of changes in internal energy that resides within the system dU, the heat added to or removed from the system dQ, and the work done by (or on) the system dW. The internal energy of a system U, refers, in thermodynamics, to the energy associated with motion and binding energies at the molecular level, which is represented by the thermal and binding energy described in the last chapter. Note that other forms of energy at the macroscopic level, particularly kinetic and potential energy, are not accounted for by the internal energy. In the following considerations, we refer to the internal energy as the thermal energy of the system, in contrast to the total energy of a system, U tot , which refers to all types of energy that are being considered. The first law is schematically shown for a simple system in Fig. 3.1a. Mathematically, it is expressed as dU = dQ − dW (3.1) In some texts, the symbols δQ and δW are used rather than dQ and dW, to indicate that these terms reflect processes that depend on the way in which energy is added and work is performed. This is typically referred to as path dependence, an aspect that we will not deal with here. We will rather focus on the first law in the following as a formulation of energy conservation. The sign convention in this formulation is that when the system performs work, that is, it generates another form of energy that is not accounted for by U outside 3.2 The First Law of Thermodynamics 49 G other G dU dW dQ J out J in D Heat engine G D Other form of energy Form of energy b.
eBook - PDF- Donald T. Haynie(Author)
- 2008(Publication Date)
- Cambridge University Press(Publisher)
There is a close resemblance to the conservation of matter, according to which the total amount of matter in a chemical reaction is a constant. The First Law of Ther-modynamics is empirical in nature; it cannot be derived from more basic principles. Unlike the Pythagorean theorem, 6 for example, which can be derived from the most basic principles of Euclidean geometry, 7 there is no mathematical proof that the First Law of Thermodynamics is right. So then why should you believe it? Sed solum ego ipse dixi ? Some might question an appeal to “authority” in scientific circles. We accept the First Law on a number of different bases, a most important and necessary one being that it is based on the experience of many, many researchers. The First Law has been tested many times, and as far as anyone knows, it has not been violated even once. It works. It’s simple. It makes sense. That alone does not prove that the First Law is true , but it does at least give a good reason for thinking that it is probably a pretty good description of nature. So we believe in the First Law of the thermodynamics. Despite its lack of a rigorous mathematical foundation, the First Law is the basis of all quantitative accounts of energy, regardless of form. The First Law makes energy the most scientific important concept in physics. And to the extent that physics is the basis of all of science and engineering, energy is the most important scientific concept in these technical areas. We saw in the previous chapter, the energy of a system can be converted from one form to another and distributed in a myriad of ways. And now we assume that energy is Fig. 2.1 The Zeroth Law of Thermodynamics. If three systems, A, B and C, are in physical contact, at equilibrium all three will have the same temperature. The concept of equilibrium is discussed in depth in Chapter 4 . Fig. 2.2 The First Law of Thermodynamics. The total energy of the universe is constant, no matter what changes occur within.
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 - PDFRealTime Physics: Active Learning Laboratories, Module 2
Heat and Thermodynamics
- David R. Sokoloff, Priscilla W. Laws, Ronald K. Thornton(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
Instead, we have to learn to draw system boundaries and total the mechanical work done by the system inside a boundary on its sur- roundings outside the boundary. The First Law of Thermodynamics is a very general statement of conservation of energy for thermal systems. It is not easy to verify in an introductory physics laboratory, and it is not derivable from Newton’s laws. Instead, it is an indepen- dent assertion about the nature of the physical world. There are many ways to achieve the same internal energy change, U. To achieve a small change in the internal energy of gas in a syringe, you could trans- fer a large amount of heat energy to it and then allow the gas to do work on its surroundings. Alternatively, you could transfer a small amount of heat energy to the gas and not let it do any work at all. The change in internal energy, U, could be the same in both processes. U depends only on Q W and not on Q or W alone. Question 3-7: Can you think of any situations where W is negligible and U Q? (Hint: Is it necessary to do work on a cup of hot coffee to cool it? Can you think of similar situations?) Question 3-8: How could you arrange a situation where Q is negligible and in which U W? Such situations have a special name in thermodynamics. They are called adiabatic processes. (Adiabatic means with no heat energy transferred into or out of the system.) 78 REALTIME PHYSICS: HEAT AND THERMODYNAMICS This page is intentionally left blank LAB 4: THE First Law of Thermodynamics 79 HOMEWORK FOR LAB 4: THE First Law of Thermodynamics 1. Describe what happens to the temperature of liquid water between 0 and 100°C when heat energy is transferred to it at a constant rate. 2. Describe what happens to the temperature of a water–ice mixture originally at 0°C when heat energy is transferred to it at a constant rate. Sketch a tem- perature history on the axes below. Indicate on your graph where the ice has completely melted.
eBook - PDF- William Moebs, Samuel J. Ling, Jeff Sanny(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
The approach to equilibrium for real systems is somewhat more complicated than for an ideal monatomic gas. Nevertheless, we can still say that energy is exchanged between the systems until their temperatures are the same. 3.3 | First Law of Thermodynamics Learning Objectives By the end of this section, you will be able to: • State the First Law of Thermodynamics and explain how it is applied • Explain how heat transfer, work done, and internal energy change are related in any thermodynamic process Now that we have seen how to calculate internal energy, heat, and work done for a thermodynamic system undergoing change during some process, we can see how these quantities interact to affect the amount of change that can occur. This interaction is given by the First Law of Thermodynamics. British scientist and novelist C. P. Snow (1905–1980) is credited with a joke about the four laws of thermodynamics. His humorous statement of the First Law of Thermodynamics is stated “you can’t win,” or in other words, you cannot get more energy out of a system than you put into it. We will see in this chapter how internal energy, heat, and work all play a role in the First Law of Thermodynamics. Suppose Q represents the heat exchanged between a system and the environment, and W is the work done by or on the system. The first law states that the change in internal energy of that system is given by Q − W . Since added heat increases the internal energy of a system, Q is positive when it is added to the system and negative when it is removed from the system. When a gas expands, it does work and its internal energy decreases. Thus, W is positive when work is done by the system and negative when work is done on the system. This sign convention is summarized in Table 3.1. The first law of 116 Chapter 3 | The First Law of Thermodynamics This OpenStax book is available for free at http://cnx.org/content/col12074/1.3
- Allan D. Kraus, James R. Welty, Abdul Aziz(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
As a word statement, the First Law of Thermodynamics is Q System E 2 – E 1 W FIGURE 3.8 A system with both heat and work interaction between the system and its surroundings. Energy and the First Law of Thermodynamics 47 The change of total energy (kinetic, potential, and internal) is equal to the net heat transferred to the control mass minus the work done by the control mass. We may also observe that either of Equations 3.12 and 3.13 demonstrate the conservation of energy principle: Energy may neither be created nor destroyed but may be converted from one form to another. 3.6 The Energy Balance for Closed Systems 3.6.1 Processes Equation 3.12 E 2 − E 1 = Q − W (3.12) indicates that over a time interval ⎧ ⎨ ⎩ the change in energy content within a system ⎫ ⎬ ⎭ = ⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩ the net amount of energy transferred into the system boundary as heat ⎫ ⎪ ⎪ ⎬ ⎪ ⎪ ⎭ − ⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩ the net amount of energy transferred out of the system boundary as work ⎫ ⎪ ⎪ ⎬ ⎪ ⎪ ⎭ (3.13) Equation (3.12) may be written using total or specific quantities. We will find it con-vienient to use a form that places the properties at state 1 and the heat transfer on the left-hand side and the properties at state 2 and the work interaction on the right-hand side. This is consistent with the conventions that we have adopted for the direction of the heat flow and whether work is done on or by the system. Thus, in terms of total energy, we have 1 2 m ˆ V 2 1 + mgz 1 + U 1 + Q = 1 2 m ˆ V 2 2 + mgz 2 + U 2 + W (J) (3.14a) or in terms of specific energy, 1 2 ˆ V 2 1 + gz 1 + u 1 + Q m = 1 2 ˆ V 2 2 + gz 2 + u 2 + W m (J/kg) (3.14b) We may write Equation 3.13 as E = Q − W Then, over some time interval, this becomes E t = Q t − W t and in the limit as t −→ 0 dE dt = ˙ Q − ˙ W (3.15) With dE dt = d KE dt + d PE dt + dU dt
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- David Ball(Author)
- 2014(Publication Date)
- Cengage Learning EMEA(Publisher)
The explicit statement of this is considered the First Law of Thermodynamics: For an isolated system, the total energy of the system remains constant. This does not mean that the system itself is static or unchanging. Something may be occurring in the system, such as a chemical reaction or the mixing of two gases. But if the system is isolated, the total energy of the system does not change. There is a mathematical way of writing the first law, using the internal energy: For an isolated system, D U 5 0 (2.10) For an infinitesimal change, equation 2.10 can be written as dU 5 0 instead. This statement of the first law has limited utility, because in studying systems we usually allow matter or energy to pass to and from the system and the surroundings. In particular, we are interested in energy changes of the system. In all investigations of energy changes in systems, it has been found that when the total energy of a system changes, the energy change goes into either work or heat, nothing else. Mathematically, this is written as D U 5 q 1 w (2.11) Equation 2.11 is another way of stating the first law. Note both the simplicity and the importance of this equation. The change in the internal energy for a process is equal to the work plus the heat. Only work or heat (or both) will accompany a change in internal energy. Because we know how to measure work and heat, we can keep track of changes in the total energy of a system. The following example illustrates. Here we are including the conversion factor between joules and liter . atmospheres. 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- H J Kreuzer, Isaac Tamblyn;;;(Authors)
- 2010(Publication Date)
- WSPC(Publisher)
In a thermodynamic system the energy can be changed by two fundamentally different methods: (a) by applying forces doing work, e.g. pushing a piston into a cylinder filled with a gas: or (b) by transferring heat into the system, e.g. by submersing the gas cylinder into a hot or a cold bath, or by heating it up with a torch. To quantify this statement we recall (2.10) that a change in energy can be achieved by work or heat transfer dU = d ¯ W + d ¯ Q (3.1) or, for a finite change, U fin = U in + W i → f + Q i → f (3.2) Heat transfer is at the center of thermodynamics and sets it apart from any other physical theory. The work performed on a system can be mechanical, electrical, magnetic, or chemical. The Laws of Thermodynamics 39 Fig. 3.1 The headstone of a great thermodynamicist, Ludwig Boltzmann, in the Central cemetery in Vienna. Remark 3.2. Energy conservation plays a fundamental role in all of physics. Indeed, an apparent violation of energy conservation is taken as an indication that some new phenomena have not been taken into account. Three examples should explain the point: (a) In a system of charged par-ticles subject to electric and magnetic fields or electromagnetic radiation, the accelerating particles emit electromagnetic radiation. Thus mechanical energy is not conserved, instead one must add the energy of the electro-magnetic field to obtain energy conservation. (b) In relativistic mechanics energy can be converted into mass. Thus only the sum of energy and mass satisfy energy conservation. (c) Looking at tracks of cosmic rays in a cloud chamber, the kinetic energies of decaying particles (obtained from the cir-cular tracks in a magnetic field) suggested the presence of uncharged and 40 Thermodynamics very light particles called neutrinos. Again a violation of energy conserva-tion lead to new discoveries. Newton’s law of energy conservation is obviously a bold abstraction that seems to be in contradiction to common experience.
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.
- Anastasios Tsonis(Author)
- 2007(Publication Date)
- Cambridge University Press(Publisher)
The other is through transfer of heat. More on that will follow soon. According to (4.1) the units for work are those of energy. Thus, the unit for work in the MKS system is the joule which is defined as J = N m where the newton N = kg m s −2 . In the cgs system, the unit is the erg which is defined as erg = dyn cm where dyn = g cm s −2 . It follows that 1 joule = 10 7 erg. 4.2 Definition of energy The First Law of Thermodynamics expresses the principle of con- servation of energy for thermodynamical systems. The idea here is that energy cannot be created or destroyed. It can only change from one form to another. In this regard if during a transforma- tion the energy of the system increases by some amount, then this amount is equal to the amount of energy the system receives from its surroundings in some other form. Let us consider a closed system contained in an adiabatic enclosure. In this case the energy of the system, U , is equal to the sum of the potential and kinetic energy of all its molecules. The sum of the energies of all molecules depends on the state of the system at a given moment (i.e. on the values p, V, T ) but obviously is indepen- dent of past states. It follows that the internal energy of the system depends on the state in which it exists but not on the way it arrived at that state. Thus, in a transformation i → f, ΔU = U f − U i . Then, for a cyclic transformation, ΔU = 0 which means that for an infinitesimal process dU is an exact differential. If no external forces are acting upon the system (i.e. the system is at equilibrium 30 4 THE First Law of Thermodynamics Figure 4.3 The work done by an external force on a system that is taken adiabatically from a reference state O or a reference state O to a state A. In this case the work done depends on the initial and final states, not on the particular path from an initial state to a final state. O ′ –W A ad′ A ad –W A –W O′ ad O with its environment), then its energy remains the same (ΔU = 0).
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