Thermodynamics: Four Laws That Move the Universe

Citation preview

Topic Science & Mathematics

Subtopic Physics

Thermodynamics: Four Laws That Move the Universe Cou urse Guidebook Professor Jeffrey C. Grossman Ma assachusetts Institute ute of Technol Techno olog logy ogy

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Jeffrey C. Grossman, Ph.D. Professor in the Department of Materials Science and Engineering Massachusetts Institute of Technology

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rofessor Jeffrey C. Grossman is a Professor in the Department of Materials Science and Engineering at the Massachusetts Institute of Technology. He received his B.A. in Physics from Johns Hopkins University in 1991 and his M.S. in Physics from the University of Illinois at Urbana-Champaign in 1992. After receiving his Ph.D. in Physics in 1996 from the University of Illinois at Urbana-Champaign, he performed postdoctoral work at the 8QLYHUVLW\ RI &DOLIRUQLD %HUNHOH\ DQG ZDV RQH RI ¿YH VHOHFWHG IURP  to be a Lawrence Fellow at the Lawrence Livermore National Laboratory. During his fellowship, he helped to establish their research program in nanotechnology and received both the Physics Directorate Outstanding 6FLHQWL¿F$FKLHYHPHQW$ZDUGDQGWKH6FLHQFHDQG7HFKQRORJ\$ZDUG Professor Grossman returned to UC Berkeley as director of a nanoscience center and head of the Computational Nanoscience research group, which he founded and which focuses on designing new materials for energy DSSOLFDWLRQV +H MRLQHG WKH 0,7 IDFXOW\ LQ WKH VXPPHU RI  DQG OHDGV a research group that develops and applies a wide range of theoretical and experimental techniques to understand, predict, and design novel materials with applications in energy conversion, energy storage, and clean water. Examples of Professor Grossman’s current research include the development of new, rechargeable solar thermal fuels, which convert and store the Sun’s energy as a transportable fuel that releases heat on demand; the design of QHZPHPEUDQHVIRUZDWHUSXUL¿FDWLRQWKDWDUHRQO\DVLQJOHDWRPWKLFNDQG lead to substantially increased performance; three-dimensional photovoltaic panels that when optimized deliver greatly enhanced power per area footprint of land; new materials that can convert waste heat directly into electricity; greener versions of one of the oldest and still most widely used building i

materials in the world, cement; nanomaterials for storing hydrogen safely and at high densities; and the design of a new type of solar cell made entirely out of a single element. As a teacher, Professor Grossman promotes collaboration across disciplines WR DSSURDFK VXEMHFW PDWWHU IURP PXOWLSOH VFLHQWL¿F SHUVSHFWLYHV $W 8& Berkeley, he developed two original classes: an interdisciplinary course in modeling materials and a course on the business of nanotechnology, which combined a broad mix of graduate students carrying out cuttingedge nanoscience research with business students eager to seek out exciting venture opportunities. At MIT, he developed two new energy courses, taught both undergraduate and graduate electives, and currently teaches a core undergraduate course in thermodynamics. To further promote collaboration, Professor Grossman has developed entirely new ways to encourage idea generation and creativity in interdisciplinary science. He invented speedstorming, a method of pairwise idea generation that works similarly to a round-robin speed-dating technique. Speedstorming combines an explicit purpose, time limits, and one-on-one encounters to create a setting where boundary-spanning opportunities can be recognized, ideas can be generated at a deep level of interdisciplinary specialty, and potential collaborators can be quickly assessed. By directly comparing speedstorming to brainstorming, Professor Grossman showed that ideas from speedstorming are more technically specialized and that speedstorming participants are better able to assess the collaborative potential of others. In test after test, greater innovation is produced in a shorter amount of time. Professor Grossman is a strong believer that scientists should teach more broadly—for example, to younger age groups, to the general public, and to teachers of varying levels from grade school to high school to community college. To this end, he has seized a number of opportunities to perform outreach activities, including appearing on television shows and podcasts; lecturing at public forums, such as the Exploratorium, the East Bay Science Cafe, and Boston’s Museum of Science; developing new colloquia series with Berkeley City College; and speaking to local high school chemistry teachers about energy and nanotechnology.

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The recipient of a Sloan Research Fellowship and an American Physical 6RFLHW\ )HOORZVKLS 3URIHVVRU *URVVPDQ KDV SXEOLVKHG PRUH WKDQ  VFLHQWL¿F SDSHUV RQ WKH WRSLFV RI VRODU SKRWRYROWDLFV WKHUPRHOHFWULFV hydrogen storage, solar fuels, nanotechnology, and self-assembly. He has appeared on a number of television shows and podcasts to discuss new materials for energy, including PBS’s Fred Friendly Seminars, the Ecopolis program on the Discovery Channel’s Science Channel, and NPR’s On Point with Tom Ashbrook. He holds 18 current or pending U.S. patents. Professor Grossman’s previous Great Course is Understanding the Science for Tomorrow: Myth and RealityŶ

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Table of Contents

INTRODUCTION Professor Biography ............................................................................i Course Scope .....................................................................................1 LECTURE GUIDES LECTURE 1 Thermodynamics—What’s under the Hood........................................5 LECTURE 2 Variables and the Flow of Energy .....................................................12 LECTURE 3 Temperature—Thermodynamics’ First Force ...................................19 LECTURE 4 Salt, Soup, Energy, and Entropy ......................................................26 LECTURE 5 The Ideal Gas Law and a Piston ......................................................32 LECTURE 6 Energy Transferred and Conserved .................................................38 LECTURE 7 Work-Heat Equivalence ....................................................................45 LECTURE 8 Entropy—The Arrow of Time ............................................................52 LECTURE 9 The Chemical Potential ....................................................................59 LECTURE 10 Enthalpy, Free Energy, and Equilibrium ...........................................65 iv

Table of Contents

LECTURE 11 Mixing and Osmotic Pressure...........................................................71 LECTURE 12 How Materials Hold Heat ..................................................................77 LECTURE 13 How Materials Respond to Heat .......................................................83 LECTURE 14 Phases of Matter—Gas, Liquid, Solid...............................................90 LECTURE 15 Phase Diagrams—Ultimate Materials Maps .....................................97 LECTURE 16 Properties of Phases ......................................................................103 LECTURE 17 To Mix, or Not to Mix? .....................................................................110 LECTURE 18 Melting and Freezing of Mixtures ................................................... 116 LECTURE 19 7KH&DUQRW(QJLQHDQG/LPLWVRI(I¿FLHQF\....................................123 LECTURE 20 More Engines—Materials at Work ..................................................129 LECTURE 21 The Electrochemical Potential ........................................................135 LECTURE 22 Chemical Reactions—Getting to Equilibrium..................................141 LECTURE 23 The Chemical Reaction Quotient....................................................147 v

Table of Contents

LECTURE 24 The Greatest Processes in the World.............................................154 SUPPLEMENTAL MATERIAL Bibliography ....................................................................................161

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Thermodynamics: Four Laws That Move the Universe

Scope:

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n this course on thermodynamics, you will study a subject that connects deep and fundamental insights from the atomic scale of the world all the way to the highly applied. Thermodynamics has been pivotal for most of the technologies that have completely revolutionized the world over the past \HDUV

The word “thermodynamics” means “heat in motion,” and without an understanding of heat, our ability to make science practical is extremely limited. Heat is, of course, everywhere, and putting heat into motion was at the core of the industrial revolution and the beginning of our modern age. The transformation of energy of all forms into, and from, heat is at the core of the energy revolution and fundamentally what makes human civilization thrive today. Starting from explaining the meaning of temperature itself, this course will FRYHU D PDVVLYH DPRXQW RI VFLHQWL¿F NQRZOHGJH (DUO\ RQ \RX ZLOO OHDUQ the crucial variables that allow us to describe any system and any process. Sometimes these variables will be rather intuitive, such as in the case of pressure and volume, while other times they will be perhaps not so intuitive, as in the case of entropy and the chemical potential. Either way, you will work toward understanding the meaning of these crucial variables all the way down to the scale of the atom and all the way up to our technologies, our buildings, and the planet itself. And you will not stop at simply learning about the variables on their own; rather, you will strive to make connections between them. Once you have a solid understanding of the different variables that describe the world of thermodynamics, you will move on to learn about the laws WKDWELQGWKHPWRJHWKHU7KH¿UVWODZRIWKHUPRG\QDPLFVLVDVWDWHPHQWRI conservation of energy, and it covers all of the different forms of energy SRVVLEOH LQFOXGLQJ WKHUPDO HQHUJ\:KHQ \RX OHDUQ WKH ¿UVW ODZ \RX ZLOO GLVFRYHUWKHPDQ\GLIIHUHQWZD\VLQZKLFKHQHUJ\FDQÀRZLQWRRURXWRID 1

material. By taking a look under the hood of materials and peering across vast length and time scales, you will learn that at the fundamental level, for WKHHQHUJ\VWRUHGLQWKHPDWHULDOLWVHOIDOOHQHUJ\ÀRZVDUHHTXLYDOHQW You will learn that internal energy represents a kind of energy that is stored inside of a material and that it can tell us how that material holds onto energy from heat and responds to changes in temperature. In addition, you will learn how a change in temperature represents a crucial driving force for heat to ÀRZ²DFRQFHSWDOVRNQRZQDVWKH]HURWKODZRIWKHUPRG\QDPLFV )URP WKH ¿UVW ODZ DQG \RXU NQRZOHGJH RI WKH LQWHUQDO HQHUJ\ \RX ZLOO understand that performing work on a system—for example, applying a pressure or initiating a reaction—is entirely equivalent to adding heat. This is one of the fundamental pillars of thermodynamics. And armed with this knowledge, you will see that there are many different ways to manipulate the properties of materials and that you can adapt your processing techniques to whatever is most convenient given the tools you have on hand.

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You will learn that vast amounts of heat can be generated not just by lighting ¿UH EXW DOVR E\ RWKHU PHDQV VXFK DV WKH IULFWLRQ RI WZR SLHFHV RI PHWDO rubbing together. And by understanding the relationships between the basic variables pressure, temperature, volume, and mass, you will learn how heat can go the other way, converting into some form of useful work. For example, taking advantage of the fact that heat makes a gas expand, which in WXUQFDQEHXVHGWRSXVKRQDSLVWRQ\RXZLOOOHDUQDERXWKRZWKHYHU\¿UVW engines were made. As you explore thermodynamics beyond the driving force and corresponding response of a material, you will learn what it is that governs when and why the system stops being driven. In other words, you will learn why a system comes to equilibrium. This means that, given any set of external conditions—such as temperature, pressure, and volume—on average, the system no longer undergoes any changes. The concept of equilibrium is so important in thermodynamics that a good portion of the early lectures of the course will be dedicated to explaining it. But it is not until the lecture on entropy and the second law of thermodynamics that you discover just how to ¿QGWKLVVSHFLDOHTXLOLEULXPSODFH 2

As you learn about the second law, you will understand just why it is that thermodynamics is the subject that treats thermal energy on an equal footing with all of the other forms: The reason it is able to do so has to do with entropy. You will be learning a lot about entropy throughout this course because it is of absolutely fundamental importance to this subject. Entropy is the crucial link between temperature and thermal energy. It is a way to quantify how many different ways there are to distribute energy, and as you will learn, it is the foundation for the second law of thermodynamics. By understanding entropy, you will gain an intuitive sense for the connectedness of thermal energy to all other forms of energy, and you will understand why a perpetual-motion machine can never exist. Entropy offers nothing less than the arrow of time, because it is the thermodynamic variable that provides a way to predict which direction all processes will occur. And you will learn that like temperature, entropy can have an absolute minimum value, as stated in the third law of thermodynamics. Once you have learned these laws, you will be able to apply them to the understanding of a wide range of properties and processes—for example, how materials change their phase between gas, liquid, and solid in many different ways and sometimes even possess completely new phases, as in the FDVHRIDVXSHUFULWLFDOÀXLG