Second Law of Thermodynamics Changes occurring in natural systems always proceed in such a way that the total amount of entropy in the universe is either unchanged or increased. If total disorder is increased, the process is irreversible. Chapter 12- The Law of Increasing Disorder Student Versions: Nature Makes Messes If You Think Things Are Bad Now, Just Wait a While The moral of the story It takes work (energy) to straighten up messes. If you increase order in one place, disorder increases someplace else to more than make up for it. Reading quiz What s Entropy? State the law of increasing disorder Total disorder of the universe increases or remains the same. It only remains the same in perfectly reversible processes. Another Of the quantities listed below, the one which is associated with the most disorder is: a. Sunlight b. ambient thermal energy c. macroscopic kinetic energy d. internal energy of stars e. chemical potential energy C.P. Snow Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of thermodynamics [the law of increasing disorder to us]. The response was cold; it was also negative. Yet I was asking something which is the equivalent of Have you read a work of Shakespeare s? C.P. Snow Two Cultures
Main Ideas The Law of Increasing Disorder (Entropy) or the Second Law of Thermodynamics Reversible/Irreversible Processes Order and Disorder Key Questions for Chapter 12 1. Can nature run backward in time? 2. What happens to the order of a system over time? 3. What is the relationship between order and the accessibility of energy? 4. Can order be increased? 5. Is there an energy crisis? 6. Is it easy to eliminate pollution? Left alone - Things tend to fall apart. Everything is made up of molecules molecules tend to get mixed up. The more Mixed, the later the time.... the arrow of time... Nature does not run backward Nothing we ve seen so far says why. a. Reversible process - one which works in reverse, one whose effect you can undo without using energy. b. Irreversible process - one you cannot undo or run in reverse unless you add energy to the system. Almost all spontaneous events in nature are irreversible irreversible reversible (almost) scrambling eggs ice <-> liquid at 0 o C smashing china real falling balls a pendulum swinging balls falling in a vacuum before they hit the ground A $100 word EntropyEntropy (disorder) Can order ever increase (Entropy decrease)? Yes - locally. But for the universe as a whole, disorder increases.
Boltzmann: Think of it this way -- Any arrangement of particles is equally probable. Only a few are what we would call ordered. Most are what we would call disordered. What are the chances that an explosion in a printing press would spontaneously generate the Book of Mormon? Does the 2 nd law mean it is impossible to print the Book of Mormon? How does the 2 nd law apply? You have to use energy to organize the type into words. Types of order Type of Energy Energy hierarchy Structure Shape Function Arrangement Mixed versus sorted Order and Energy Order in a system is related to the accessibility of its energy. (accessibility - how easy is it to use the energy to do work?) The more ordered the system, the more accessible is its energy. NOTE: Energy is conserved - but may be easier or harder to use to get somewhere. Energy hierarchy Form of Energy Gravitational Potential / Macroscopic Kinetic Nuclear Potential Electrical (Household) Chemical Potential Thermal Energy (heat) (Microscopic KE) ordered disordered Why are KE and GPE more ordered? All of the atoms have the same amount of energy Why is thermal energy the least ordered? The atoms are moving in random directions at random speeds.
Structure What has more order, a house before or after a hurricane knocks it over? What has more order, the contents of a leftover container before or after it s sat in the fridge for a few months? What has more order, your computer keyboard before or after your roommate spills pop on it? Arrangement What has more order, this set of letters or Jsadhjf dl;dfj teoiznt ajsdjfp twe kjdlka? What has more order, the ink and water before or after they get mixed? What has more order, a jar of hot water and a jar of cold water, or 2 jars of warm water? Which came first? A Why is A less ordered? A. Because the ice molecules are mixed with the water molecules. B. Because the hot molecules are mixed with the cold molecules C. Because the electrical energy in the ice got turned into thermal energy A B B Completely reversible processes Contain frictionless surfaces. Perfectly insulated systems. Happen infinitely slowly. Have odd starting and ending points. No real process that uses energy is perfectly reversible. SO. Can you use the 2 nd law to prove that it is impossible to clean your room? A. Yes, even though it looks neater, it is really more disordered after you pick it up B. No, it is possible to clean your room, but doing so is bad for the universe as a whole. C. No, the second law doesn t apply when there are people involved.
What about life? Life is highly ordered. Does the 2 nd law mean that life couldn t happen naturally? Increasing order You can increase order in part of a system. When you do, something or some part of the universe becomes even more disorganized so that the total disorder is increased. Examples: Refrigerator Car Engine Example: Refrigerator Which is more ordered warm outside and cold inside or all the same temp.? Compressor and condenser cool down the air inside the fridge. an ordering process use highly organized electrical energy which is turned into thermal energy that heats up the room a disordering process Which is greater? Example: Automobile Chemical potential energy in fuel Thermal Energy Macroscopic K.E. + Thermal energy (Hot gases from combustion) Efficiency = % of input energy which is converted to useful, desired energy. Auto ~25% efficient. For every $1 you spend on gas, get 25 cents of motion. No heat engine is 100% efficient. WHY? Why is that? What is highest in the energy hierarchy? Can you convert 100% of CPE into KE? Can you convert 100% of CPE into heat? How does the car get KE out of thermal energy? Law of increasing disorder (different form) Any form of energy can be totally converted to any other form which has the same or more disorder, but it cannot be totally converted to another form in which it would have less disorder. Some of the energy is wasted heating up the environment.
Lots of energy in air molecules. So... Dude, why not run the refrigerator using the energy in the air? Remember the little dudes are bouncing around at 700mph. Random thermal energy is not ordered. Can t make it flow to create a more disordered system. What if there is a temperature difference? How about hotter air to colder or hotter water to colder? Universal Heat Death This is the way the world ends, not with a bang but a whimper. T.S. Eliot The Pollution Problem Several ways to reduce pollution: 1. Reduce industrial production 2. Eliminate cars 3. Increase efficiency of machines to their theoretical limit. 4. Collect pollutants after they are produced The Energy Crisis 1. Is there a total energy crisis? NO! - total mass-energy is always conserved 2. Is there a useful energy crisis? YES! - burning fossil fuels loses order irreversibly - resulting thermal energy is not very accessible Quizlet In a reversible process, the total amount of disorder a. is zero b. becomes infinite c. stays the same d. decreases e. increases Equilibrium When left to themselves, all systems change to the arrangement with maximum disorder. This state of maximum disorder is called Equilibrium. No further spontaneous macroscopic changes occur once the system is in equilibrium.