1. Heat Transfer and the 2 nd Law of Thermodynamics

2. Warm Up 1 10 A sample liquid is cooled from 150°C to 30°C, causing the liquid to change into a solid. Which of the following has occurred? F Chemical composition has changed. G A physical change has occurred. H A new compound has formed. J Evaporation of a solvent has occurred.

3. Heat Transfer Heat Transfer Heat flows from _______________.Heat flows from _______________. To reverse the process, work must be done.To reverse the process, work must be done.

4. Heat Transfer Heat Transfer The amount of heat absorbed (Q) is equal to the amount of heat released (-Q).The amount of heat absorbed (Q) is equal to the amount of heat released (-Q). Q = - Q Q = - Q mcΔT = mc-(ΔT) ; ( -Tf + Ti) mcΔT = mc-(ΔT) ; ( -Tf + Ti) mc (Tf-Ti) = mc (Ti –Tf ) mc (Tf-Ti) = mc (Ti –Tf ) The final temperature for both will be the same. (Thermal Equilibrium)The final temperature for both will be the same. (Thermal Equilibrium)

5. Heat Transfer Positive Q value if -energy is absorbed, added, required, needed Negative Q value if - energy is released, removed

6. Heat Transfer ExampleExample A 50 g metal bolt (c bolt = 899 J/kg o C) is dropped into a 150 ml of water. The initial temperature of the water is 21 o C and they both reached an equilibrium temperature of 25 o C. What is the initial temperature of the bolt? Remember: energy absorbed by the water is equal to energy released by the metal bolt.

7. Solution Q water = - Q bolt (released energy) Q water = - Q bolt (released energy) m w c w (Tf - Ti) = m b c b (Ti-Tf) m w c w (Tf - Ti) = m b c b (Ti-Tf) (0.15 kg)(4186 J/kg o C)(25 o C – 21 o C) = (0.05 kg)(899 J/kg o C)(Ti - 25 o C) (0.15 kg)(4186 J/kg o C)(4 o C) = (0.05 kg)(899 J/kg o C) (Ti - 25 o C) (0.15 kg)(4186 J/kg o C)(4 o C) = (0.05 kg)(899 J/kg o C) (Ti - 25 o C) 2511.6 J = (44.95 J/ o C) (Ti - 25 o C) 2511.6 J = (44.95 J/ o C) (Ti - 25 o C) 2511.6 J = (Ti - 25 o C) 2511.6 J = (Ti - 25 o C) (44.95 J/ o C) (44.95 J/ o C) 55.88 o C = Ti - 25 o C 55.88 o C + 25 o C = Ti 55.88 o C + 25 o C = Ti 80.88 o C = Ti 80.88 o C = Ti

8. 2 nd Law of Thermodynamics The Law of Increased EntropyThe Law of Increased Entropy –In a closed system the entropy of the system will either remain constant or increase.

9. Law of Heat Transfer and Entropy Entropy – disorderliness of things (gas particles have more entropy than solids and liquids)Entropy – disorderliness of things (gas particles have more entropy than solids and liquids) Heat flows from higher temperature to lower temperature.Heat flows from higher temperature to lower temperature. To reverse the process, work will be done.To reverse the process, work will be done.

10. Law of Heat Transfer and Entropy Examples: 1.Ice cream easily melts but to refreeze it you need a heat pump (fridge) to do it. 2.Coffee on the table will cool down eventually at room temperature. What kind of work is needed to warm it up?

11. Entropy By doing work on a system you can decrease the system’s entropy because the work you are doing is creating orderBy doing work on a system you can decrease the system’s entropy because the work you are doing is creating order It takes a lot more work to put your room in order than to mess it up.It takes a lot more work to put your room in order than to mess it up. You will need an AC pump to cool down (reduce the entropy) of a room in Houston during summer time.You will need an AC pump to cool down (reduce the entropy) of a room in Houston during summer time.

12. Light bulb moment To reverse the process of Heat Transfer work must be done to do it.To reverse the process of Heat Transfer work must be done to do it. To reverse or to minimize the entropy (disorderliness), work must be done.To reverse or to minimize the entropy (disorderliness), work must be done.

13. Exit Ticket If energy cannot be created and heat only flows from high to low, what would happen to the universe far, far, far in the future?

14. Universal Thermal Equilibrium “Heat Death”“Heat Death” Eventually everything in the universe will be at thermal equilibrium as energy is dissipated (lost).Eventually everything in the universe will be at thermal equilibrium as energy is dissipated (lost). If everything is at the same temperature, work will be impossible.If everything is at the same temperature, work will be impossible. Work