DOCSLIB.ORG

Heat and the Second Law of Thermodynamics

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Heat and the Second Law of Thermodynamics 1st and 2nd law of Thermodynamics crucial for understanding all sciences Heat and the Second Law of Thermodynamics Chapter 4 Great Idea: Heat is a form of energy that flows from warmer to cooler objects Chapter Outline • Nature’s Direction • Coming to Terms with Heat • Heat Transfer • The Second Law of Thermodynamics • Consequences of the Second Law Nature’s Direction Second Law of Thermodynamics Coming to Terms with Heat Heat and Temperature • Heat – Energy in motion – Warm to cool • Temperature – Atomic movement • Temperature Scales – Fahrenheit scale – Celsius – Kelvin • Absolute zero Comparison of Temperature Scales Temperature Conversions • Conversion to Fahrenheit: – °F = (1.8 x °C) + 32 • Conversion to Celsius: – °C = (°F – 32)/1.8 Specific Heat Capacity • Specific heat capacity – Quantity of heat needed to raise 1g of a substance by 1 °C • Water – Highest specific heat – 1 cal/g °C Heat Transfer Heat Transfer • Conduction – Movement of heat by atomic-scale collision – Thermal conductivity • Convection – Bulk transfer of molecules – Convection cell • Radiation Conducon Infrared Imaging Detects Heat Loss Convecon Technology • Home Insulation The Science of Life • Animal Insulation and Feathers The Science of Life • Temperature Regulation The Second Law of Thermodynamics The Second Law of Thermodynamics – Heat does not flow spontaneously from cold to hot – No engine can exclusively convert heat to work – Every isolated system tends toward disorder Heat Will Not Flow Spontaneously from a Cold to a Hot Body Can you do it??? Efficiency of an Engine • Determined by the second law of thermodynamics Every Isolated System Becomes More Disordered with Time • Ordered System – Regular predictable pattern • Disordered System – Random • Entropy – Measure of disorder – The entropy of an isolated system remains constant or increases Highly Ordered Regular vs. Disordered Patterns Consequences of the Second Law The Arrow of Time • Four dimensions – 3 have no directionality – The 4th has direction • Time – Second law and time Built-in Limitations of the Universe • The Second Law’s consequences – Some things cannot happen – Fossil fuels – Hierarchy of energy The Science of Life • Evolution and the Second Law of Thermodynamics Let’s go back to Energy…. How do we get energy from fossil fuels? One example…. ThinkQuest How Do Fossil Fuels and Biomass Pollute? All fossil fuels and biomasses consist of carbon and hydrogen atoms. When these fuels are burned, or "combusted," carbon atoms unite with oxygen in the air to form carbon dioxide. Energy content of various fuels: Energy from fuels Direct heat, lighting Run an engine….Heat, Other work Unit of energy is Joules What is the problem???????? Efficiency Engines: Efficiency = work done/energy put into the system = What you got out/What you put in 100% efficiency not possible…. friction, viscosity insulation other A heat engine is a physical or theoretical device that converts thermal energy to mechanical output. The mechanical output is called work, and the thermal energy input is called heat. Think of an engine as operating between two thermal reservoirs… One at High Temperature…engine takes the heat (QH from hot reservoir) does work with it and returns the rest to the cooler reservoir… Energy Conservation………………………. QH=Work + QC If you want engine to operate you must provide QH Efficiency = W/QH No perfect engines………….. We can only convert some of the heat to work not all of it……… 2nd Law of Thermodynamics……………… Entropy ……………Time Travel …………… “Beam me up Scotty” ………….. “perfume “ Example: In the US, 85% of the electricity is generated by burning fossil fuels to produce steam, Which in turn drives alternators that produce electricity. Power plants can produce steam with a temperature as high as 6000C by pressurizing the steam. The resulting waste heat must be exhausted into the environment at a temperature of 200 C (1- Tcold/Thot)x 100%= maximum efficiency 600+273=873 degree Kelvin 20 + 273=293 1-(293/873) x 100%=66.4% Real power plants…………….40% So…what does this mean for energy? Electricity is a manufactured product. It is not something you pump out of the ground or mine or collect from the sun or wind. Electric power is manufactured from a rotating machine that we call an electrical generator. After it is generated, (manufactured) it is then delivered through copper wires to where it is utilized But the invention of the machine to generate power is right next to the invention of the printing press in the list of major contributions to the advancement of human civilization. A "generator" and "motor" are essentially the same thing: what you call it depends on whether electricity is going into the unit or coming out of it. Electric generators are essentially very large quantities of copper wire spinning around inside very large magnets, at very high speeds. Example: A commercial utility electric generator -- for example, a 180-megawatt generator -- can be quite large. It is 20 feet in diameter, 50 feet long, and weighs over 50 tons. The copper coils (called the "armature") spin at 3600 revolutions per minute. Although the principle is simple (copper wire and magnets), it's not necessarily easy! Steam turbine generators, gas turbine generators, diesel engine generators, alternate energy systems (except photovoltaics), even nuclear power plants all operate on the same principle - magnets plus copper wire plus motion equals electric current. The electricity produced is the same, regardless of source. .
Load more

Recommended publications
  • Lecture 4: 09.16.05 Temperature, Heat, and Entropy
    3.012 Fundamentals of Materials Science Fall 2005 Lecture 4: 09.16.05 Temperature, heat, and entropy Today: LAST TIME .........................................................................................................................................................................................2� State functions ..............................................................................................................................................................................2� Path dependent variables: heat and work..................................................................................................................................2� DEFINING TEMPERATURE ...................................................................................................................................................................4� The zeroth law of thermodynamics .............................................................................................................................................4� The absolute temperature scale ..................................................................................................................................................5� CONSEQUENCES OF THE RELATION BETWEEN TEMPERATURE, HEAT, AND ENTROPY: HEAT CAPACITY .......................................6� The difference between heat and temperature ...........................................................................................................................6� Defining heat capacity.................................................................................................................................................................6�
    [Show full text]
  • HEAT and TEMPERATURE Heat Is a Type of ENERGY. When Absorbed
    HEAT AND TEMPERATURE Heat is a type of ENERGY. When absorbed by a substance, heat causes inter-particle bonds to weaken and break which leads to a change of state (solid to liquid for example). Heat causing a phase change is NOT sufficient to cause an increase in temperature. Heat also causes an increase of kinetic energy (motion, friction) of the particles in a substance. This WILL cause an increase in TEMPERATURE. Temperature is NOT energy, only a measure of KINETIC ENERGY The reason why there is no change in temperature at a phase change is because the substance is using the heat only to change the way the particles interact (“stick together”). There is no increase in the particle motion and hence no rise in temperature. THERMAL ENERGY is one type of INTERNAL ENERGY possessed by an object. It is the KINETIC ENERGY component of the object’s internal energy. When thermal energy is transferred from a hot to a cold body, the term HEAT is used to describe the transferred energy. The hot body will decrease in temperature and hence in thermal energy. The cold body will increase in temperature and hence in thermal energy. Temperature Scales: The K scale is the absolute temperature scale. The lowest K temperature, 0 K, is absolute zero, the temperature at which an object possesses no thermal energy. The Celsius scale is based upon the melting point and boiling point of water at 1 atm pressure (0, 100o C) K = oC + 273.13 UNITS OF HEAT ENERGY The unit of heat energy we will use in this lesson is called the JOULE (J).
    [Show full text]
  • Heat Energy a Science A–Z Physical Series Word Count: 1,324 Heat Energy
    Heat Energy A Science A–Z Physical Series Word Count: 1,324 Heat Energy Written by Felicia Brown Visit www.sciencea-z.com www.sciencea-z.com KEY ELEMENTS USED IN THIS BOOK The Big Idea: One of the most important types of energy on Earth is heat energy. A great deal of heat energy comes from the Sun’s light Heat Energy hitting Earth. Other sources include geothermal energy, friction, and even living things. Heat energy is the driving force behind everything we do. This energy gives us the ability to run, dance, sing, and play. We also use heat energy to warm our homes, cook our food, power our vehicles, and create electricity. Key words: cold, conduction, conductor, convection, energy, evaporate, fire, friction, fuel, gas, geothermal heat, geyser, heat energy, hot, insulation, insulator, lightning, liquid, matter, particles, radiate, radiant energy, solid, Sun, temperature, thermometer, transfer, volcano Key comprehension skill: Cause and effect Other suitable comprehension skills: Compare and contrast; classify information; main idea and details; identify facts; elements of a genre; interpret graphs, charts, and diagram Key reading strategy: Connect to prior knowledge Other suitable reading strategies: Ask and answer questions; summarize; visualize; using a table of contents and headings; using a glossary and bold terms Photo Credits: Front cover: © iStockphoto.com/Julien Grondin; back cover, page 5: © iStockphoto.com/ Arpad Benedek; title page, page 20 (top): © iStockphoto.com/Anna Ziska; pages 3, 9, 20 (bottom): © Jupiterimages Corporation;
    [Show full text]
  • TEMPERATURE, HEAT, and SPECIFIC HEAT INTRODUCTION Temperature and Heat Are Two Topics That Are Often Confused
    TEMPERATURE, HEAT, AND SPECIFIC HEAT INTRODUCTION Temperature and heat are two topics that are often confused. Temperature measures how hot or cold an object is. Commonly this is measured with the aid of a thermometer even though other devices such as thermocouples and pyrometers are also used. Temperature is an intensive property; it does not depend on the amount of material present. In scientific work, temperature is most commonly expressed in units of degrees Celsius. On this scale the freezing point of water is 0oC and its boiling point is 100oC. Heat is a form of energy and is a phenomenon that has its origin in the motion of particles that make up a substance. Heat is an extensive property. The unit of heat in the metric system is called the calorie (cal). One calorie is defined as the amount of heat necessary to raise 1 gram of water by 1oC. This means that if you wish to raise 7 g of water by 4oC, (4)(7) = 28 cal would be required. A somewhat larger unit than the calorie is the kilocalorie (kcal) which equals 1000 cal. The definition of the calorie was made in reference to a particular substance, namely water. It takes 1 cal to raise the temperature of 1 g of water by 1oC. Does this imply perhaps that the amount of heat energy necessary to raise 1 g of other substances by 1oC is not equal to 1 cal? Experimentally we indeed find this to be true. In the modern system of international units heat is expressed in joules and kilojoules.
    [Show full text]
  • Lecture 6: Entropy
    Matthew Schwartz Statistical Mechanics, Spring 2019 Lecture 6: Entropy 1 Introduction In this lecture, we discuss many ways to think about entropy. The most important and most famous property of entropy is that it never decreases Stot > 0 (1) Here, Stot means the change in entropy of a system plus the change in entropy of the surroundings. This is the second law of thermodynamics that we met in the previous lecture. There's a great quote from Sir Arthur Eddington from 1927 summarizing the importance of the second law: If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equationsthen so much the worse for Maxwell's equations. If it is found to be contradicted by observationwell these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of ther- modynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation. Another possibly relevant quote, from the introduction to the statistical mechanics book by David Goodstein: Ludwig Boltzmann who spent much of his life studying statistical mechanics, died in 1906, by his own hand. Paul Ehrenfest, carrying on the work, died similarly in 1933. Now it is our turn to study statistical mechanics. There are many ways to dene entropy. All of them are equivalent, although it can be hard to see. In this lecture we will compare and contrast dierent denitions, building up intuition for how to think about entropy in dierent contexts. The original denition of entropy, due to Clausius, was thermodynamic.
    [Show full text]
  • Symptoms of Heat- Related Illness How to Protect Your
    BE PREPARED FOR EXTREME HEAT Extreme heat often results in the highest annual number of deaths among all weather-related disasters. FEMA V-1004/June 2018 In most of the U.S., extreme heat is a long period (2 to 3 days) of high heat and humidity with temperatures above 90 degrees. Greater risk Can happen anywhere Humidity increases the feeling of heat as measured by a heat index IF YOU ARE UNDER AN EXTREME HEAT WARNING Check on family members Find air conditioning, if possible. and neighbors. Avoid strenuous activities. Drink plenty of fluids. Watch for heat cramps, heat Watch for heat illness. exhaustion, and heat stroke. Wear light clothing. Never leave people or pets in a closed car. HOW TO STAY SAFE WHEN EXTREME HEAT THREATENS Prepare Be Safe Recognize NOW DURING +RESPOND Find places in your community where Never leave a child, adult, or animal Know the signs and ways to treat you can go to get cool. alone inside a vehicle on a warm day. heat-related illness. Try to keep your home cool: Find places with air conditioning. Heat Cramps Libraries, shopping malls, and • Signs: Muscle pains or spasms in • Cover windows with drapes community centers can provide a cool the stomach, arms, or legs. or shades. place to take a break from the heat. • Actions: Go to a cooler location. • Weather-strip doors and Wear a If you’re outside, find shade. Remove excess clothing. Take windows. hat wide enough to protect your face. sips of cool sports drinks with salt and sugar. Get medical help if • Use window reflectors such as Wear loose, lightweight, light- cramps last more than an hour.
    [Show full text]
  • Module P7.4 Specific Heat, Latent Heat and Entropy
    FLEXIBLE LEARNING APPROACH TO PHYSICS Module P7.4 Specific heat, latent heat and entropy 1 Opening items 4 PVT-surfaces and changes of phase 1.1 Module introduction 4.1 The critical point 1.2 Fast track questions 4.2 The triple point 1.3 Ready to study? 4.3 The Clausius–Clapeyron equation 2 Heating solids and liquids 5 Entropy and the second law of thermodynamics 2.1 Heat, work and internal energy 5.1 The second law of thermodynamics 2.2 Changes of temperature: specific heat 5.2 Entropy: a function of state 2.3 Changes of phase: latent heat 5.3 The principle of entropy increase 2.4 Measuring specific heats and latent heats 5.4 The irreversibility of nature 3 Heating gases 6 Closing items 3.1 Ideal gases 6.1 Module summary 3.2 Principal specific heats: monatomic ideal gases 6.2 Achievements 3.3 Principal specific heats: other gases 6.3 Exit test 3.4 Isothermal and adiabatic processes Exit module FLAP P7.4 Specific heat, latent heat and entropy COPYRIGHT © 1998 THE OPEN UNIVERSITY S570 V1.1 1 Opening items 1.1 Module introduction What happens when a substance is heated? Its temperature may rise; it may melt or evaporate; it may expand and do work1—1the net effect of the heating depends on the conditions under which the heating takes place. In this module we discuss the heating of solids, liquids and gases under a variety of conditions. We also look more generally at the problem of converting heat into useful work, and the related issue of the irreversibility of many natural processes.
    [Show full text]
  • 3. Energy, Heat, and Work
    3. Energy, Heat, and Work 3.1. Energy 3.2. Potential and Kinetic Energy 3.3. Internal Energy 3.4. Relatively Effects 3.5. Heat 3.6. Work 3.7. Notation and Sign Convention In these Lecture Notes we examine the basis of thermodynamics – fundamental definitions and equations for energy, heat, and work. 3-1. Energy. Two of man's earliest observations was that: 1)useful work could be accomplished by exerting a force through a distance and that the product of force and distance was proportional to the expended effort, and 2)heat could be ‘felt’ in when close or in contact with a warm body. There were many explanations for this second observation including that of invisible particles traveling through space1. It was not until the early beginnings of modern science and molecular theory that scientists discovered a true physical understanding of ‘heat flow’. It was later that a few notable individuals, including James Prescott Joule, discovered through experiment that work and heat were the same phenomenon and that this phenomenon was energy: Energy is the capacity, either latent or apparent, to exert a force through a distance. The presence of energy is indicated by the macroscopic characteristics of the physical or chemical structure of matter such as its pressure, density, or temperature - properties of matter. The concept of hot versus cold arose in the distant past as a consequence of man's sense of touch or feel. Observations show that, when a hot and a cold substance are placed together, the hot substance gets colder as the cold substance gets hotter.
    [Show full text]
  • Thermodynamic Temperature
    Thermodynamic temperature Thermodynamic temperature is the absolute measure 1 Overview of temperature and is one of the principal parameters of thermodynamics. Temperature is a measure of the random submicroscopic Thermodynamic temperature is defined by the third law motions and vibrations of the particle constituents of of thermodynamics in which the theoretically lowest tem- matter. These motions comprise the internal energy of perature is the null or zero point. At this point, absolute a substance. More specifically, the thermodynamic tem- zero, the particle constituents of matter have minimal perature of any bulk quantity of matter is the measure motion and can become no colder.[1][2] In the quantum- of the average kinetic energy per classical (i.e., non- mechanical description, matter at absolute zero is in its quantum) degree of freedom of its constituent particles. ground state, which is its state of lowest energy. Thermo- “Translational motions” are almost always in the classical dynamic temperature is often also called absolute tem- regime. Translational motions are ordinary, whole-body perature, for two reasons: one, proposed by Kelvin, that movements in three-dimensional space in which particles it does not depend on the properties of a particular mate- move about and exchange energy in collisions. Figure 1 rial; two that it refers to an absolute zero according to the below shows translational motion in gases; Figure 4 be- properties of the ideal gas. low shows translational motion in solids. Thermodynamic temperature’s null point, absolute zero, is the temperature The International System of Units specifies a particular at which the particle constituents of matter are as close as scale for thermodynamic temperature.
    [Show full text]
  • Section 13.4 Temperature-Energy Graphs Temperature-Energy Graphs
    Section 13.4 Temperature-Energy Graphs Temperature-Energy Graphs A temperature-energy graph shows the energy and temperature changes as water turns from a solid, ice, to a liquid, water, and finally to a gas, water vapor. Water Phase Change Graph F D 100 E gas liquid Temperature º C. º Temperature B 0 C solid A Heat (thermal energy) Phase Change Diagram – Flat Line • Anytime there is a flat line on a temp-energy graph, a phase change is occurring. Water Phase Change Graph F D condensing 100 boiling E Temperature º C. º Temperature B freezing 0 melting C A Heat (thermal energy) Temperature-Energy Graphs Calculating Energy of a Phase Change Heat of Fusion (solid - liquid) Heat of Fusion: The amount of energy absorbed or released when a substance melts or freezes. • Symbol: LF • The LF for water is 334 J/g • This is the quantity of heat that must be absorbed by each gram of ice at 0°C to convert it to water at 0°C • This is the quantity of heat that must be released from each gram of water at 0°C to convert it to ice at 0°C Heat of Fusion (solid - liquid) Heat of Fusion: • Varies for different substances • All the energy is used to increase the potential energy of the particles. (Break bonds) • Average kinetic energy doesn’t change Heat of Fusion (solid - liquid) Heat of Fusion: Q = m·Lf Heat of Fusion Heat Mass Heat of Vaporization (liquid – gas) Heat of Vaporization: The amount of energy absorbed or released when a substance boils or condenses.
    [Show full text]
  • Discipline in Thermodynamics
    energies Perspective Discipline in Thermodynamics Adrian Bejan Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27708-0300, USA; [email protected] Received: 24 April 2020; Accepted: 11 May 2020; Published: 15 May 2020 Abstract: Thermodynamics is a discipline, with unambiguous concepts, words, laws and usefulness. Today it is in danger of becoming a Tower of Babel. Its key words are being pasted brazenly on new concepts, to promote them with no respect for their proper meaning. In this brief Perspective, I outline a few steps to correct our difficult situation. Keywords: thermodynamics; discipline; misunderstandings; disorder; entropy; second law; false science; false publishing 1. Our Difficult Situation Thermodynamics used to be brief, simple and unambiguous. Today, thermodynamics is in a difficult situation because of the confusion and gibberish that permeate through scientific publications, popular science, journalism, and public conversations. Thermodynamics, entropy, and similar names are pasted brazenly on new concepts in order to promote them, without respect for their proper meaning. Thermodynamics is a discipline, a body of knowledge with unambiguous concepts, words, rules and promise. Recently, I made attempts to clarify our difficult situation [1–4], so here are the main ideas: The thermodynamics that in the 1850s joined science serves now as a pillar for the broadest tent, which is physics. From Carnot, Rankine, Clausius, and William Thomson (Lord Kelvin) came not one but two laws: the law of energy conservation (the first law) and the law of irreversibility (the second law). The success of the new science has been truly monumental, from steam engines and power plants of all kinds, to electric power in every outlet, refrigeration, air conditioning, transportation, and fast communication today.
    [Show full text]
  • Prevent Heat Illness at Work Poster
    Prevent Heat Illness at Work Outdoor and indoor heat exposure can be dangerous. Ways to Protect Yourself and Others Ease into Work. Nearly 3 out of 4 fatalities from heat illness happen during the first week of work. 100% New and returning workers need to build tolerance to heat (acclimatize) and take frequent breaks. 20% Follow the 20% Rule. On the first day, work no more than 20% of the shift’s duration at full intensity in the heat. Increase the duration of time at full intensity by no more than 20% a day until workers are used to working in the heat. MON TUE WED THU FRI Drink Cool Water Dress for the Heat Drink cool water even if you are not thirsty — at least Wear a hat and light-colored, loose-fitting, and 1 cup every 20 minutes. breathable clothing if possible. Take Rest Breaks Watch Out for Each Other Take enough time to recover from heat given the Monitor yourself and others for signs of temperature, humidity, and conditions. heat illness. If Wearing a Face Covering Find Shade or a Cool Area Change your face covering if it gets wet or soiled. Take breaks in a designated shady or cool location. Verbally check on others frequently. First Aid for Heat Illness The following are signs of a medical emergency! Abnormal thinking or behavior ?? ? ? ? ? Slurred speech Seizures 9-1-1 Loss of consciousness 1 CALL 911 IMMEDIATELY 2 COOL THE WORKER RIGHT AWAY WITH WATER OR ICE 3 STAY WITH THE WORKER UNTIL HELP ARRIVES Watch for any other signs of heat illness and act quickly.
    [Show full text]