1 / 59

Ch. 10 Thermodynamics

Ch. 10 Thermodynamics. Internal Energy can be used to do work. Delta U = Delta Q - Delta W Example: heating a gas, the gas does work on the surroundings. Gas does work On the air Outside the Balloon.

mara-peters
Download Presentation

Ch. 10 Thermodynamics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ch. 10 Thermodynamics

  2. Internal Energy can be used to do work. • Delta U = Delta Q - Delta W • Example: heating a gas, the gas does work on the surroundings.

  3. Gas does work On the air Outside the Balloon.

  4. Negative Work is done when you compress a gas. Positive work is done when the gas expands.

  5. Heat and work are energy transferred to or from a system. • You must always take into account the entire environment when you consider energy transfers.

  6. Remember Total energy in the universe is CONSTANT.

  7. Example: We supply work energy to the cart. Have we created energy in the universe? Where did the energy come from? Where does it go?

  8. Work done on or by a gas is pressure * volume change. • W = P*deltaV

  9. What is the work done by a gas that is at 5,000 Pa and changes volume from 1.5 to 2 m^3? What is the work done ON a gas that is at 5,000 Pa and changes volume from 5 m^3 to 4 m^3?

  10. What if the pressure is increased but there is no change in volume? • No work is done.

  11. What happens when temperature changes but not volume? • There is no work done.

  12. Processes where there is no change in volume are called isovolumetric processes.

  13. Isothermal Process One in which temp. is constant.

  14. Heat Work Slowly inflating a balloon and adding heat as you do = Isothermal. The temperature and internal energy stays constant.

  15. Isothermal processes must occur SLOWLY.

  16. Adiabatic Processes must occur Quickly. • In these processes, no energy is transferred as heat in either direction.

  17. The expanding gas loses internal energy as it expands. It does work on the surrounding air.

  18. 1st Law of Thermodynamics • Energy Conservation Delta U = Q - W • See page 342. 0 = ∆U + ∆KE + ∆PE Mechanical energy lost goes to U (faster moving molecules)

  19. See Table 1, page 343. Be very careful about sign of W.

  20. 100 C outside piston, 30 C inside. Which way does Q flow? What does delta U =? 30 100

  21. 30 C outside piston, 100 C inside. Which way does Q flow? What does delta U =? 100 30

  22. What is the sign of W? What does delta U =?

  23. What is the sign of W? What does delta U =?

  24. Problem B, Page 345.

  25. Cyclic Processes The system will return to where it started. (Like refrigerators and engines).

  26. See figure 8, page 347. The net work that a heat engine can do in any cycle = Qh – Qc.

  27. End of notes for now.

  28. Drawing activity Expanding Gas, Compressed Gas, Isothermal Process

  29. How does a Fridge work?

  30. 1.) Refrigerant is heated. It will boil.

  31. 2. Refrigerant is compressed. Temperature increases.

  32. 3. Refrigerant is moved outside the fridge, where it gives up heat to the air. It liquefies.

  33. 4. Refrigerant is allowed back into the fridge. It is expanded and its temperature decreases.

  34. Compressor and Expansion Valve

  35. The Second Law of Thermodynamics Things almost always occur in order for a positive change in entropy to happen. • Entropy (S) (J/K) A measure of the randomness or relative probability of a system.

  36. Efficiency of Heat Engines a heat engine absorbs energy from a high-temperature body as heat, does work on the environment, and then gives up energy to a low-temperature body as heat.

  37. For a heat engine: • Wnet = Qnet = Qh - Qc

  38. No cyclic process that converts heat entirely into work is possible. • The engine must eventually give off heat energy to a lower temperature source.

  39. Perpetual Motion Machines

  40. Efficiency of a heat engine EQUATIONS, see page 353.

  41. Sample Problem C, Page 354

  42. Debunking Entropy • The entropy in the universe is always increasing. • A process will be spontaneous if it creates a positive change in entropy.

  43. If I blow some carbon dioxide in the air, which result will give a positive ∆S? • A.) All the carbon dioxide will clump up and enventually condense into a solid. • B.) The carbon dioxide will spread out evenly.

  44. If I flip this water bottle on its side, how will the water molecules arrange themselves? (Which will result in an increase in entropy?) • A.) They will line up and create the word “banana” • B. ) They will spread out evenly.

  45. The greater a system’s entropy, the greater its: Disorder, Randomness, and Probability.

  46. Ice to Water Vapor

More Related