1. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Ch 12 - Heat This false-color thermal image (an infrared photo) shows where energy is escaping from a house by heat transfer, because it is colder outside than inside. In this chapter we investigate the connection between heat and energy. Chapter Goal: To expand our understanding of energy to include the energy transfer mechanism of heat.

2. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. 12.2 The Kelvin Temperature Scale A constant-volume gas thermometer.

3. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. 12.2 The Kelvin Temperature Scale absolute zero point = -273.15 o C

4. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Our model of energy: E mech = K + U In this chapter, we will look at another kind of energy, and another kind of energy transfer function.

5. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Internal Energy, U int Let’s look at another type of energy of a system, its internal energy, U int. This consists of : microscopic motion of atoms and molecules potential energy of molecular bonds U int can be transferred in or out of a system, via a non- mechanical energy transfer function called HEAT (Q).

6. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Heat (Q) is an energy transfer mechanism that operates when the system is put in contact with a hotter or colder environment

7. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Heat, Temperature, and Thermal Energy Internal Energy U int is an energy of the system due to the motion of its atoms and molecules. Any system has an internal energy even if it is isolated and not interacting with its environment. The units of U int are Joules. Heat Q is energy transferred between the system and the environment as they interact due to a temperature difference between them. A temperature difference is required in order for heat to be transferred between the system and the environment. The units of Q are Joules. Temperature T is a state variable that quantifies the “hotness” or “coldness” of a system. The units of T are degrees Celsius or Kelvin. Temperature is not the same as heat

8. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Heat and Equilibrium Temperature Heat (Q) is an energy transfer mechanism analogous to work. Energy is transferred by work when force is applied (macroscopic). Energy is transferred by heat (Q) when collisions occur between faster moving molecules and slower moving molecules (microscopic). Energy transfer via heat will stop when all interacting objects are at the same temperature.

9. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. The sign of heat, Q

10. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Heat added to the system If energy is added to the system due to heat only, and the system is not moving, the increase in energy will manifest itself in one of two ways: change in temperature change in phase

11. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Temperature Change and Specific Heat Capacity The temperature change of a substance due to heat is: ∆T = Q/(mc) where Q is heat (in joules), m is mass (in kg) and c is called the specific heat capacity of that substance. The symbol for specific heat capacity is c. The specific heat capacity is the amount of energy that raises the temperature of 1 kg of a substance by 1 K (or 1 °C) and has units of Joules/kg K or Joules/kg °C. The above equation is often written: Q = mc ∆T

12. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Specific heat capacity problem The specific heat capacity of gold (c gold ) = 129 J/kg K. How much heat is required to raise the temperature of 500 g of gold from 10 0 to 50 0 C?

13. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Specific heat capacity problem The specific heat capacity of gold (c gold ) = 129 J/kg K. How much heat is required to raise the temperature of 500 g of gold from 10 0 to 50 0 C? Answer: Q = 2580 Joules It was not necessary to convert to Kelvin since the calculation requires ΔT.

14. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Objects A and B are brought into close thermal contact with each other, but they are well isolated from their surroundings. Initially T A = 0°C and T B = 100°C. The specific heat of A is more than the specific heat of B. The two objects will soon reach a common final temperature T f. The final temperature is: A. T f > 50°C. B. T f < 50°C. C. T f = 50°C.

15. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. EOC #51 A 0.25-kg coffee mug is made from a material that has a specific heat capacity of 950 J/(kg · C°) and contains 0.30 kg of water. The cup and water are at 25° C. To make a cup of coffee, a small electric heater is immersed in the water and brings it to a boil in two minutes. Assume that the cup and water always have the same temperature and determine the minimum power rating of this heater. Q h = m w c w ∆T w + m c c c ∆T c

16. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. EOC #51 A 0.25-kg coffee mug is made from a material that has a specific heat capacity of 950 J/(kg · C°) and contains 0.30 kg of water. The cup and water are at 25° C. To make a cup of coffee, a small electric heater is immersed in the water and brings it to a boil in two minutes. Assume that the cup and water always have the same temperature and determine the minimum power rating of this heater. Q h = m w c w ∆T w + m c c c ∆T c P = 930 W

17. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Calorimetry – Conservation of Energy Two (or more) systems, at different temperatures are placed in contact, but isolated from the environment. These systems will eventually reach a common equilibrium temperature without energy loss.

18. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Problem-solving strategy for Calorimetry Problems Identify the interacting systems and verify that they are isolated from the environment (Code language: insulated container). List known information and identify what you need to find. Convert quantities to SI units, and volumes to mass. Calorimetry problems are a statement of conservation of energy: Q net = Q 1 + Q 2 + Q 3 + … = 0 Q = m c (T f – T 0 ) for each system. Do not automatically put the higher temperature first! Assess your answer. T f that is higher or lower than all initial conditions is an indication of an error, usually with signs.

19. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Calorimetry example with 3 materials A precious stone dealer wishes to find the specific heat capacity of a 0.030 kg gemstone. The specimen is heated to 95.0° C and placed in a 0.15 kg copper vessel containing 0.080 kg water at equilibrium (with the copper) at 25.0°C. There is negligible loss to the environment. When equilibrium is established (with the gemstone, the temperature is 28.5°C. What is the specific heat capacity of the gemstone?

20. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Calorimetry example with 3 materials A precious stone dealer wishes to find the specific heat capacity of a 0.030 kg gemstone. The specimen is heated to 95.0° C and placed in a 0.15 kg copper vessel containing 0.080 kg water at equilibrium (with the copper) at 25.0°C. There is negligible loss to the environment. When equilibrium is established (with the gemstone, the temperature is 28.5°C. What is the specific heat capacity of the gemstone? Answer: 689 J/kg K

21. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Phase Change and Latent Heat

22. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Phase change and latent heat A phase change is characterized by a change in thermal energy without a change in temperature. The temperature vs. heat graph shows that during the phase changes, the temperature does not change, although heat energy continues to be added.

23. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Phase Change and Latent Heat The amount of heat energy that causes 1 kg of substance to undergo a phase change is called the latent heat of that substance. The symbol for latent heat of transformation is L. The units of latent heat are Joules/kg.

24. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Phase Change and Latent Heat It takes more energy to change a liquid into a vapor, than to change a solid into a liquid. To do the former, we use the latent heat of vaporization, L v. To do the latter, we use the latent heat of fusion, L f.

25. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Phase Change and Latent Heat The heat required for the entire system of mass m to undergo a phase change is: Q = ±mL f melt/freeze Q = ±mL v evaporate/condense the ± sign indicates that heat must be added to the system during melting and evaporation and removed from the system during freezing and condensation.

26. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Latent Heats of fusion and vaporization: It takes a lot of energy to change phase

27. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. EOC #67 Ice at -10.0°C and steam at 130°C are brought together at atmospheric pressure in a perfectly insulated container. After thermal equilibrium is reached, the liquid phase at 50.0°C is present. Ignoring the container and the equilibrium vapor pressure of the liquid at 50.0°C, find the ratio of the mass of steam to the mass of ice. The specific heat capacity of steam is 2020 J/(kg · C°), the specific heat capacity of ice is 2.00 x10 3 J/(kg·C°), and the specific heat capacity of water is 4186 J/(kg·C°).

28. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. EOC #67 Ice at -10.0°C and steam at 130°C are brought together at atmospheric pressure in a perfectly insulated container. After thermal equilibrium is reached, the liquid phase at 50.0°C is present. Ignoring the container and the equilibrium vapor pressure of the liquid at 50.0°C, find the ratio of the mass of steam to the mass of ice. The specific heat capacity of steam is 2020 J/(kg · C°), the specific heat capacity of ice is 2.00 x10 3 J/(kg·C°), and the specific heat capacity of water is 4186 J/(kg·C°). Ans:.223

29. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley. Prelab Question #2 You have 100 g of water in an aluminum calorimeter cup that has a mass of 25 g. Both water and aluminum have come to thermal equilibrium at 21° C. What will be the final temperature of the mixture if 10 g of 0 ° ice is added?