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Energy

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Energy

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  1. 0 Energy

  2. Energy 0 • Energy (E) is the ability to do work. • Many types, but we can say 3 main types: • Radiant • Potential • Kinetic

  3. US Energy Consumption by Source

  4. 0 Radiant Energy • Light Energy • Visible and Invisible • Travels in waves over distances • Electromagnetic waves • Waves that spread out in all directions from the source • Visible light, UV light, Infra Red Radiation, X-rays, microwaves, radio waves

  5. 0 Potential Energy (PE) • Stored Energy • Due to position • Gravitational PE • Elastic PE • Chemical bonds • Chemical PE • Nuclear energy • Fuels • Attractions between molecules

  6. 0 Kinetic Energy (KE) • Energy of motion • Atomic vibrations • Molecular movement • Vibration • Rotation • Translation • Movement of subatomic particles

  7. Kinetic Energy Can be calculated:

  8. How are each type shown here? • Radiant • Rainbow = visible light • Kinetic • Windmill moving • Potential • All molecules store energy • Water in clouds • Air • Materials the windmill is made from, the plants at the bottom

  9. Temperature Scales: Measuring that Thermal Energy

  10. A Note on the Fahrenheit Scale • NEVER use it in this class. Ever. Only Belize and the US use this scale. • Gabriel Fahrenheit made great thermometers. His scale was replicated the world over because of this. But if you stop and think about it, does 32°F for freezing make sense, or 212°F for boiling? 180 degrees separates them. • 100 degrees, as in the Celcius scale (sometimes called the Centigrade scale) makes much more sense. • Fahrenheit based 0°F on the freezing point of water mixed with NH4Cl, and 32°F for freezing water, and 96°F for human body temperature (he was off by 2.6°). Why? Because he felt like it and it was easy to draw lines at those intervals. • (According to a letter Fahrenheit wrote to his friend Herman Boerhaave,[8] his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer’s scale, brine freezes at 0 degrees, ice melts at 7.5 degrees, body temperature is 22.5, and water boils at 60 degrees. Fahrenheit multiplied each value by four in order to eliminate fractions and increase the granularity of the scale. He then re-calibrated his scale using the melting point of ice and normal human body temperature (which were at 30 and 90 degrees); he adjusted the scale so that the melting point of ice would be 32 degrees and body temperature 96 degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power). I took this from Wikipedia.

  11. Kelvin Temperatures • Based on absolute zero (0 K, -273 oC) • The temperature at which ALL KE stops • NO molecular motion. • Lowest temperature theoretically possible • Can’t really get there in real life • (See 3rd Law of Thermodynamics in a few slides) • K = oC + 273 • Technically 273.14, but we can stop at 3 significant digits

  12. Why do we need the Kelvin scale? • Two reasons • We need a scale that is relative to molecular motion for certain topics • You can’t use negative numbers to indicate motion when it IS present • -20°C makes NO sense in light of indicating motion • And 40°C ISN’T twice as much motion as 20°C, • (40K IS twice the motion of 20K) • Because when working with equations, can’t use zero • We get undefined answers if we divide • We get answers of 0 if we multiple • And those answers would NOT make sense if compared to answers calculated with a positive or negative number

  13. Energy (E): The ability to do work Exergy: The energy availableto do work No symbol Entropy (S): The measure of the disorder of a system Enthalpy(H): The thermal energy (heat) content of a system The 4 Es: Energy, Exergy, Entropy, & Enthalpy There will be more on these!

  14. Thermodynamics • The study of energy flow • inter-relation between heat, work, and energy of a system • Summary of the three laws: • The energy in the universe is constant • Things get more disorganized over time in a system until everything is equal • You can’t reach absolute zero

  15. 1st Law of Thermodynamics • The energy in the universe is constant • E=mc2 • Law of Conservation Matter • Matter can not be created or destroyed • Law of Conservation of Energy • Energy can not be created or destroyed • However, matter and energy can both change forms in chemical reactions • Can also interconvert between matter and energy in NUCLEAR reactions (more on this later this year.) Summed up: You can not win. You can’t get something for nothing because energy and matter are conserved.

  16. Energy Time

  17. Before the 2nd Law… • Entropy (S) is a measure of DISORGANIZATION in a system (this simply put; there is a much more complicated description about the unavailable energy to do work) • Anything disorganized has higher entropy than something organized • Exergy is the Energy available to do work

  18. 2nd Law of Thermodynamics • Things get more disorganized over time in a system until everything equilibrium is reached (everything is equal) • Heat flows from hot to cold, not the reverse • Law of Entropy • By nature, things get more disorganized to spread out energy and matter • The quality of the energy (which is exergy) decreases over time Summed up: You can not break even. You can not return to the same energy state because things get more disorganized (gain entropy)

  19. Exergy and Energy • The energy of the universe is constant, but exergy is constantly consumed. This can be compared with a tooth-paste tube: When you squeeze the tube (= conduct any process) the paste (= exergy) comes out. You can never put the paste back in the tube again (try!), and in the end you have only the tube itself (= low-exergy) left. • When you squeeze the tube, the depressions (= entropy) will increase. (The entropy of a system increases when exergy is lost) But you can never take the depressions in the tube and 'un-brush' your teeth. (I.e. entropy is not negative exergy.) • When you buy energy from the electricity network, you actually buy exergy. You can find the energy as room temperature heat after some time, but you can not take that room temperature energy back to the electricity company and ask for money back. They won't accept it.

  20. Energy and Matter Gain Entropy Over Time

  21. Exergy: The Energy available to do work

  22. 3rd Law of Thermodynamics • You can’t reach absolute zero and expect things to happen • At absolute zero, all kinetic motion ceases. And that energy needs to go somewhere. It goes to something else. And gets transferred back until everything is at an equal temperature. Summed up: You can not get out of the game, because absolute zero is unobtainable.

  23. Law of Conservation of Energy 0 • Energy cannot be created or destroyed…but it CAN change forms. • Example: Burning wood in a fire • The energy in chemical bonds is released as heat (KE and PE), light (RE), sound (KE) • These forms of energy are less useful • have less exergy

  24. 0 Radiant Energy: EM Waves Potential Energy: Stored Kinetic Energy:Motion

  25. The CPE in these items could:

  26. Rio Summer OlympicsProposed Solar Waterfall http://www.snopes.com/photos/architecture/solartower.asp

  27. Combinations of PE and KE are very common on a large scale 0 KE and PE animation

  28. PE and KE

  29. When E changes forms… • The amount of energy one thing loses is gained somewhere else. • E lost = E gained (Law of Conservation of Energy) • But the E gained is usually not all in one place (2nd Law of thermodynamics) • It is spread out (more entropy) • Often in the forms of heat and light • Which are less useful (less exergy)

  30. Energy Transformations

  31. Thermal Energy: KE + PE on the small scale • What’s up with Temperature vs Heat? • Temperature is related to the average kinetic energy of the particles in a substance.

  32. Thermal energyrelationships As temperature increases, so does thermal energy (because the energy of the particles increased). If the temperature stays the same, the thermal energy in a more massive substance is higher(because it is a total measure of energy).

  33. Cup gets cooler while hand gets warmer Heat The flow of thermal energy from one object to another. Heat always flows from warmer to cooler objects. Ice gets warmer while hand gets cooler

  34. Heat and Temperature 0 • Heat: the measure of the flow of RANDOM kinetic energy • Temperature: the measure of heat • So…temperature is a measure of kinetic energy of the particles of a substance * Sometimes heat is radiated as IR (infra-red radiation, a form of radiant energy)

  35. Thermal Energy • Thermal Energy is the total of all the (kinetic and potential) heat energy of all the particles in a substance. • PE from how the molecules are placed relative to each other (attractions) • Farther = more PE, just like how something farther off the ground has higher gravitational PE

  36. Exothermic and Endothermic Processes Endothermic Exothermic • Energy is being gained/ absorbed by the object or substance (called the system) from the surroundings • Have positive change in enthalpy values (+ΔH) • Energy is lost/ released from the object or substance (called the system) to the surroundings • Have negative change in enthalpy values (-ΔH)

  37. The big picture… • How do we see this energy cycling in the real world, and not just as a part of Chemistry class? • Around the house? • In the environment? • While thinking about a car?

  38. Cup gets cooler while hand gets warmer • If the cup is the system, it is undergoing an exothermic process because it is losing heat to the surroundings (hand) • If the ice is the system, it is undergoing an endothermic process because it is absorbing heat from the surroundings (hand) Ice gets warmer while hand gets cooler

  39. Which is process is endothermic? Which is exothermic?

  40. Trophic Levels and Energy Consumers are all heterotrophs Energy Out; 90% per level

  41. Can the world really run out of Energy? World-Wide Energy Sources, (2007)

  42. phase changes & energy

  43. Phase Diagrams • Tell what state of matter a material is in at a given temperature and pressure • The triple point is the pressure and temperature when a solid, liquid, and a gas of the same substance exist at equilibrium • Equilibrium: When there is no net change • Here referring to changes in state • Can also refer to temperature and chemicals • The critical point is the temperature above which a substance will always be a gas, regardless of pressure • Fullerton Phase Diagram Explorer Link

  44. Phase Diagrams

  45. Phase Diagram for Water

  46. A few terms • Freezing Point - The temperature at which the solid and liquid phases of a substance are in equilibrium at atmospheric pressure. • The same temperature as the melting point • Boiling Point - The temperature at which the vapor pressure of a liquid is equal to the pressure on the liquid. • Vapor Pressure- The pressure at which the vaporization rates are equal to condensation rates

  47. Phase Changes Enthalpy(H): The heat (thermal energy) content of a system

  48. States of Matter and Entropy The states are NOT plateaus because entropy is NOT constant. This isn’t a phase change diagram.

  49. Energy and Matter and Connected • Any change in matter ALWAYS is accompanied by a change in energy

  50. Phase Changes and Energy