1. 19 Second Law Thermo Heat Engines and 2 nd Law Thermodynamics Hk: 27, 35.

2. Second Law of Thermodynamics Heat flows spontaneously from a substance at a higher temperature to a substance at a lower temperature. The reverse situation does not occur spontaneously. Ex. Hot drink cools but does not reheat

3. Heat Engines Device that uses heat to perform work Hot Reservoir (e.g. steam) Cool Reservoir (e.g. pool of water) Efficiency is work done per unit of input heat (e = W/Q H ) Ex. A heat engine does 100J of work when given 300J from the hot reservoir. The efficiency is 100J/300J = 0.33 = 33%.

4. Heat Engine Flow Chart

6. Summary Heat engines use part of heat and reject rest, efficiency = work out/heat in 2 nd Law of Thermodynamics prescribes that efficiency cannot be 100% /

9. 19-2 Refrigerators and the Second Law of Thermodynamics

10. Refrigerators and the Second Law of Therm.

11. 19-3 Equivalence of the Heat- Engine and Refrigerator Statements Omit

12. 19-4 The Carnot Engine

13. Carnot Theorem

15. The Carnot Cycle Heat Engine

16. 19-5 Heat Pumps Omit

17. 19-6 Irreversibility and Disorder

18. Irreversible Processes Introduce Disorder. Example: Container of gas collides inelastically with wall. Translational kinetic energy is added to general thermal energy of gas

19. 19-7 Entropy

20. Entropy Entropy is a measure of the disorder of a system Low entropy (ordered) High entropy (disordered) Reversible Process: Entropy is constant Irreversible Process: Entropy increases

21. Second Law in terms of Entropy the total entropy of the universe does not change when a reversible process occurs. the total entropy does increase when an irreversible process occurs.

22. 19-8 Entropy and the Availability of Energy Omit

23. 19-9 Entropy and the Probability Omit

24. Summary: Heat engines accept heat and output work and heat. Refrigerators reverse this process. Carnot engine is most efficient engine. 2 nd Law of Therm. dictates the direction of natural processes. Irreversible processes increase disorder. Entropy is a measure of disorder and increases for any irreversible process.

25. Heat engines typically have efficiencies in the range 1.3% to 5% 2.20% to 60% 3.80% to 90%