Physics
Internal Energy
Internal energy refers to the total energy contained within a system, including the kinetic and potential energies of its particles. It is a measure of the system's microscopic energy and is related to the temperature of the system. Changes in internal energy can occur through heat transfer or work done on or by the system.
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10 Key excerpts on "Internal Energy"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
Internal Energy In thermodynamics, the Internal Energy is the total energy contained by a thermodynamic system. It is the energy necessary to create the system, but excludes the energy to displace the system's surroundings, any energy associated with a move as a whole, or due to external force fields. Internal Energy has two major components, kinetic energy and potential energy. The kinetic energy is due to the motion of the system's particles (translations, rotations, vibrations), and the potential energy is associated with the static constituents of matter, static electric energy of atoms within molecules or crystals, the static energy of chemical bonds. The Internal Energy of a system can be changed by heating the system or by doing work on it; the first law of thermodynamics states that the increase in Internal Energy is equal to the total heat added and work done. If the system is isolated, its Internal Energy cannot change. For practical considerations in thermodynamics or engineering it is rarely necessary, nor convenient, to consider all energies belonging to the total intrinsic energy of a sample system, such as the energy given by the equivalence of mass. Typically, descriptions only include components relevant to the system under study. Thermodynamics is chiefly concerned only with changes of the Internal Energy. The Internal Energy is a state function of a system, because its value depends only on the current state of the system and not on the path taken or process undergone to arrive at this state. It is an extensive quantity. The SI unit of energy is the joule. Sometimes physicists define a corresponding intensive thermodynamic property called specific Internal Energy , which is Internal Energy per a unit of mass of the system in question. As such, the SI unit of specific Internal Energy is J/kg. If intensive Internal Energy is expressed per amount of substance, then it is referred to as molar Internal Energy and the unit is J/mol.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
Internal Energy In thermodynamics, the Internal Energy is the total energy contained by a thermo-dynamic system. It is the energy necessary to create the system, but excludes the energy to displace the system's surroundings, any energy associated with a move as a whole, or due to external force fields. Internal Energy has two major components, kinetic energy and potential energy. The kinetic energy is due to the motion of the system's particles (translations, rotations, vibrations), and the potential energy is associated with the static constituents of matter, static electric energy of atoms within molecules or crystals, the static energy of chemical bonds. The Internal Energy of a system can be changed by heating the system or by doing work on it; the first law of thermodynamics states that the increase in Internal Energy is equal to the total heat added and work done. If the system is isolated, its Internal Energy cannot change. For practical considerations in thermodynamics or engineering it is rarely necessary, nor convenient, to consider all energies belonging to the total intrinsic energy of a sample system, such as the energy given by the equivalence of mass. Typically, descriptions only include components relevant to the system under study. Thermodynamics is chiefly concerned only with changes of the Internal Energy. The Internal Energy is a state function of a system, because its value depends only on the current state of the system and not on the path taken or process undergone to arrive at this state. It is an extensive quantity. The SI unit of energy is the joule. Sometimes physicists define a corresponding intensive thermodynamic property called specific Internal Energy , which is Internal Energy per a unit of mass of the system in question. As such, the SI unit of specific Internal Energy is J/kg. If intensive Internal Energy is expressed per amount of substance, then it is referred to as molar Internal Energy and the unit is J/mol.
- Allan D. Kraus, James R. Welty, Abdul Aziz(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
37 38 Introduction to Thermal and Fluid Engineering FORMS OF ENERGY Kinetic Energy is the energy that a body possesses by virtue of its motion. Potential Energy is the energy that a body possesses by virtue of its position. Internal Energy is a characteristic property of the state of a thermo-dynamic system including the intrinsic energies of individual molecules, kinetic energies of internal motions, and contributions from interations between individual molecules. FIGURE 3.1 Forms of energy. The Internal Energy is treated as a macroscopic quantity even though it is composed of many microscopic energies resulting from the atomic and molecular structure. Having thus observed that mass is a conserved property, we next focus our attention on the forms of energy and a general conservation of energy principle known as the first law of thermodynamics . The forms of energy are summarized in Figure 3.1. 3.2 Kinetic, Potential, and Internal Energy Macroscopic kinetic energy, gravitational potential energy (most often referred to merely as “potential energy”), and microscopic Internal Energy are scalar properties and we ex-amine them in some detail in the subsections that follow. 3.2.1 Kinetic Energy In Newton’s second law, F = ma , the acceleration can be represented by a = d ˆ V dt = d ˆ V dx dx dt = ˆ V d ˆ V dx where x is the displacement and ˆ V is the velocity in the direction of the applied force, F . If this form of the acceleration is substituted into F = ma where the applied force is constant, the result is F = m ˆ V d ˆ V dx or, after separation of the variables Fdx = m ˆ Vd ˆ V Integration between x 1 , where the velocity is ˆ V 1 , and x 2 , where the velocity is ˆ V 2 , gives Fs = m 2 ( ˆ V 2 2 − ˆ V 2 1 ) Energy and the First Law of Thermodynamics 39 Datum Level z ˆ V FIGURE 3.2 A projectile that possesses kinetic energy by virtue of its velocity and potential energy by virtue of its elevation, z, above the datum level.
eBook - PDFThermodynamics
Fundamentals and Engineering Applications
- William C. Reynolds, Piero Colonna(Authors)
- 2018(Publication Date)
- Cambridge University Press(Publisher)
Nuclear bonding energy The force fields that hold the nuclei of atoms together are much stronger than electronic forces and hence there is much more energy associated with these bonds than with the electronic bonding of molecules. This energy is released in nuclear fission or fusion reactions, where it shows up in greatly increased microscopic kinetic energy. 2.3 Internal Energy In a macroscopic system, such as the gas in an internal combustion engine or the silicon crystal in a semi-conductor device, the sum of all the energy in the hidden microscopic modes (see Figure 2.1 ) is called the Internal Energy , U , U = E translation + E vibration + E rotation + E electronic +· · · (2.1) We emphasize that Internal Energy should not be called heat , a word used properly only for something else (see Section 2.6 ). Figure 2.1 Internal Energy is the energy of the hidden microscopic modes. 2.4 Total Energy In general one can express the energy of matter as the sum of the Internal Energy arising from the hidden microscopic modes and the macroscopically observable forms of energy, E = U + E kinetic + E potential + · · · = U + 1 2 M V 2 + Mgz + · · · (2.2) Here V is the macroscopically observable velocity of the material relative to the coordinate frame, g is the gravitational acceleration, z is the height above the reference point for potential energy, and the dots represent other forms of macroscopically observable energy (electronic charge, magnetic dipoles, etc.). U includes the randomly oriented microscopic kinetic energy of the gas molecules due to motions relative to their common center of mass. Additional kinetic energy due to any coherent molecular motion that is revealed by motion of the center of mass is rep-resented by the 1 2 M V 2 term. 2.5 Energy Transfer as Work In Chapter 1 we introduced the notion of work as energy transfer.
No longer available |Learn more- Mike Pauken, Michael Pauken(Authors)
- 2011(Publication Date)
- For Dummies(Publisher)
is one of the strongest forms of molecular energy because it’s associated with the nucleus of an atom. This energy form isn’t discussed in thermodynamics at this level, but at least you know it exists.Calculating total energy
The total amount of energy that a system contains includes both the macroscopic and microscopic forms of energy associated with it. The following equations for total energy sum up the kinetic, potential, and internal energies. The extensive form of the total energy of a system includes the mass of the system in each energy component. The intensive form is on a per unit mass basis.E = KE + PE + U = 1⁄2m · V 2 + m · g · z + m · u (extensive form)e = ke + pe + u = 1⁄2V 2 + g · z + u (intensive form)Nearly every thermodynamic analysis uses one of these two equations. You use them to determine the amount of energy that occurs in the form of work and heat for many thermodynamic processes. Because chemical and nuclear energy aren’t usually dealt with in introductory thermodynamics, these forms of energy are omitted from the equations calculating the total energy of a system.Enthalpy
Many thermodynamic processes involve a fluid flowing through a device and undergoing a change in Internal Energy. Any time a fluid flows into a system, it does work on the system, and any time a fluid flows out of a system, the system does work on the fluid. This occurs when hot water flows though an automobile radiator, for example. The work associated with the fluid flowing into or out of the system is represented by the product of the pressure (P ) and the volume (V ) of the fluid. This happens in so many situations that a new property, enthalpy (H ), is used to combine the change in Internal Energy with this flow work, to make calculations more convenient. Enthalpy is defined by the following equation: H = U + PV. The units for enthalpy are the same as those for Internal Energy. The units for the pressure-volume (PV ) product in the SI system are kilopascals-cubic meter (kPa · m3
- Keith Stowe(Author)
- 2007(Publication Date)
- Cambridge University Press(Publisher)
Part III Energy and the first law Chapter 4 Internal Energy A The general idea 65 B Potential energies 65 B.1 General thoughts 65 B.2 Solids, liquids, and gases 68 C Quantum effects 69 C.1 Rotations and vibrations 69 C.2 Example --the diatomic gas molecule 70 D Degrees of freedom 70 E Equipartition 71 F Thermal energy 72 A The general idea Our investigations of larger systems begin with their Internal Energy, which involves the relative motion and interactions among the system’s own particles. It does not include interactions with or motion relative to objects outside the system. The Internal Energy of a nail, for example, would include the energy of vibra-tion of the atoms and the motions and interactions of the conduction electrons (Figure 4.1). But it would not include the nail’s potential energy or motion relative to the Earth, for example. Of course, if you enlarge the system to include both the Earth and the nail, then these would be part of the Internal Energy of this larger system, but they are not part of the Internal Energy of the nail by itself. B Potential energies We now examine the energies of the individual particles in solids, liquids, and gases, by means of models that are useful in developing intuition for these systems. B.1 General thoughts Imagine a particle that is anchored in place by interactions with its neigh-bors. We can use a Taylor series expansion (Appendix B) to write its potential 65 66 Introduction to thermodynamics and statistical mechanics Figure 4.1 (a) The Internal Energy of a nail includes such things as the vibrations of the iron atoms and the potential and kinetic energies of the conduction electrons. (b) If the nail were thrown over a cliff, its motion relative to the Earth and its potential energy due to the Earth’s gravity would not be part of its Internal Energy, because they involve more than just the nail itself.
eBook - PDF- Richard L. Myers(Author)
- 2005(Publication Date)
- Greenwood(Publisher)
The arrangement and recon- figuration of atomic nuclei is the source of nuclear potential energy. Elastic potential energy results from the deformation on an object. For example, when a spring is com- pressed or stretched, energy is stored in the spring as elastic potential energy. Kinetic energy is the energy of motion. Anything that moves possesses kinetic energy. Translational kinetic energy is equal to one-half times the product of mass and the magnitude of velocity squared: translational kinetic energy = l/2(mv 2 ) Rotational kinetic energy is equal to one-half times the product of the moment of inertial and the magnitude of rotational velocity squared: rotational kinetic energy = \/2(IOJ 2 ) The fact that translational kinetic energy is related to the square of the velocity has con- sequences during storms when wind speeds increase significantly above normal condi- tions. A 50 mph wind compared to a 10 mph wind has 25 times the kinetic energy, while hurricane winds of 100 mph would have 100 times the kinetic energy of a 10 mph wind. An object resting on the ground has zero kinetic energy and zero gravitational potential energy with respect to the Earth's surface, but it would be wrong to assume it possesses no energy. The object is made of atoms, and each atom contains electrons revolving around an atomic nucleus. By virtue of their trans- lational, rotational, and vibrational motion, atoms possess kinetic energy. Matter also pos- sesses chemical potential energy stored within chemical bonds, as mentioned previously. The Internal Energy is the sum total of the kinetic and potential energy possessed by the atoms and molecules comprising matter. Work Inherent in the definition of energy are the terms work and heat. Work and heat are transfer properties and can be considered processes that transfer energy across a sys- tem's boundary. Work can be transferred to the system across the system boundary from the surroundings or from the system to the surroundings.
eBook - PDFBasic Physical Chemistry
The Route to Understanding
- E Brian Smith(Author)
- 2012(Publication Date)
- ICP(Publisher)
2 Energy Understanding the energy of chemical systems is of crucial importance to chemists. The properties of atoms and molecules are determined, to a large extent, by the magnitudes of the various forms of energy they contain. The energy changes accompanying chemical processes are a major (but not the only) factor in determining the direction in which reactions can proceed. An understanding of energy was not easily obtained and, although the first tentative steps were made in the 17th century, it was not until the 19th century that the concept was fully established. Nowadays, the most frequently-employed general definitions of energy relate it, somewhat unhelpfully, to the capacity to raise weights. While being aware of such definitions, we will introduce energy in terms of more relevant definitions. 2.1 Kinetic and potential energy The energy possessed by bodies is of two types. The energy which arises by virtue of the motion of a body is referred to as the kinetic energy and is defined by the equation E K = m v 2 2 = p 2 2 m , where m is the mass, v the velocity and p the linear momentum, m v, of the body in motion. In addition to their kinetic energy, bodies can possess potential energy due to the forces that act on them by virtue of their position. The most common example of this is the energy that arises from gravitational forces. This energy, which depends on the height of the body in the Earth’s gravitational field, is termed the gravitational energy, V , and is given by V = mgh , where g is the acceleration due to gravity, which depends somewhat on location but is approximately 9.81 m s − 2 . The kinetic energy of a body at rest is zero. However, the zero of potential energy is arbitrary 17 18 | Basic Physical Chemistry and can be set at a convenient point. Thus, it is a common convention to regard the gravitational potential energy at the surface of the Earth as zero.
eBook - PDFGeneral Chemistry I as a Second Language
Mastering the Fundamental Skills
- David R. Klein(Author)
- 2015(Publication Date)
- Wiley(Publisher)
133 CHAPTER 5 ENERGY AND ENTHALPY This chapter is the first part of a much larger topic called thermodynamics. You will revisit thermodynamics in more detail during the second semester of chemistry. The topics in this chapter will lay the foundation that you need for the second semester, so it is important to master the terms, concepts, and problem-solving techniques in this chapter. If you don’t get these topics down now, you will find yourself strug- gling with thermodynamics next semester. In one sentence, thermodynamics is the study of energy and its interconver- sions. Put more simply, thermodynamics is the study of how, why, and when en- ergy can be transferred from one place to another. In this chapter we focus on how energy is transferred. In the second semester of chemistry, you will learn about why and when energy is transferred (entropy and free energy). The first half of this chapter will focus on theory, terminology, and analogies. The second half of the chapter will focus on problem-solving techniques. 5.1 ENERGY We will start off our discussion with the different types of energy, but as we do so, keep in mind that we have still not defined what energy really is. We will get to the definition a bit later. Energy can be classified into the following categories: kinetic energy and po- tential energy. Kinetic energy is energy associated with motion (or velocity), and potential energy is energy associated with position. Let’s start with kinetic energy. When a soccer ball is in motion, it has kinetic energy (you might even remember the term 1 ⁄ 2 mv 2 from your high school physics class). When the soccer ball hits another ball, it will transfer some of its energy to the other ball. Molecules can do the same thing. A molecule in motion has kinetic energy that it can transfer when it collides with another molecule.
- S. Bobby Rauf(Author)
- 2021(Publication Date)
- River Publishers(Publisher)
Law of Conservation of Energy The law of conservation of energy states that energy can be con-verted from one form to another but cannot be created or destroyed . This can be expressed, mathematically, as: 8 Thermodynamics Made Simple for Energy Engineers ∑ E = ∑ Energy = Constant Table 1-3. Rankin Temperature Conversion Formulas Table 1-4. Kelvin Temperature Conversion Factors FORMS OF ENERGY IN MECHANICAL AND THERMODYNAMIC SYSTEMS Potential Energy Potential energy is defned as energy possessed by an object by vir-tue of its height or elevation. Potential energy can be defned, mathemati-cally, as follows: E potential = m.g.h, {SI Units} Eq. 1-8 E potential = m.(g/g c ).h, US Units} Eq. 1-8a When the change in potential energy is achieved through performance of work, W : W = Δ E potential Eq. 1-9 9 Introduction to Energy, Heat, and Thermodynamics Kinetic Energy Kinetic energy is defned as energy possessed by an object by virtue of its motion. Kinetic energy can be defned, mathematically, as follows: E kinetic = ½.m.v 2 {SI Units} Eq. 1-10 E kinetic = ½. (m/g c ). v 2 {US Units} Eq. 1-10a Where, m = mass of the object in motion v = velocity of the object in motion g c = 32 lbm-ft/lbf-s 2 When the change in kinetic energy is achieved through performance of work, W : W = Δ E kinetic Eq. 1-11 Energy Stored in a Spring 2 Potential energy can be stored in a spring—or in any elastic object— by compression or extension of the spring. Potential energy stored in a spring can be expressed, mathematically, as follows: E spring = ½.k.x 2 Eq. 1-12 And, W spring = Δ E spring Eq. 1-13 Where, k = The spring constant x = The contraction or expansion of the spring 2 Note: In steel beam systems, beams act as springs, when loaded, to a certain degree. The defection of a beam would represent the “ x ,” in Eq. 1-11. Pressure Energy Energy stored in a system in form of pressure is referred to as pres- 10 Thermodynamics Made Simple for Energy Engineers sure energy.
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