1. CH. 12 Thermal Energy Sec. 12.1: Temperature & Thermal Energy

2. Thermodynamics The study of heat and its relation to work and energy

3. HOT vs. COLD Caloric Theory: 18 th Century belief in an invisible fluid that called “caloric” that flows into hot bodies. – Explained why hot metals expand – Could not explain why hands get warm when rubbed Kinetic Molecular Theory: In a hot body, particles move faster (greater KE), than particles in cold water.

4. Thermal Energy vs. Temperature… Thermal Energy = Heat (Q): – total energy of molecular motion in a substance Depends on size and mass Temperature – average energy of molecular motion in a substance Does not depend on size or mass Can one object have more heat, but a lower temperature than another object? Hot cup of water vs. the ocean

5. Temperature Scales To convert from Celsius to Kelvin, add 273.15 To convert from Kelvin to Celsius, subtract 273.15

6. Heat “Flow” Law of conservation of energy: Energy is not created or destroyed, ONLY TRANSFERRED! Heat (Q) is transferred from one object to another due to temperature difference. Heat always flows from warmer object to cooler object! If Q = negative heat has left the object If Q = positive heat has been absorbed by the object

7. 3 Types of Heat Transfers

8. Units for Heat calorie: heat needed to raise 1.0 gram of water 1.0ᵒC 1 Calorie = 1 kilocalorie = 1000 calories Ex. Kudos Bar 130 Calories = 130 kcal = 130,000 calories Joule – SI unit for energy 1 J = 0.2390 cal 4.184 J = 1 cal How many joules are in a Kudos bar?

9. Specific Heat Specific Heat: Amount of heat needed to increase the temperature of 1g of a substance exactly 1ᵒC. specific heat (C) = Heat (Joules or calories) Mass (grams) x change in temperature (C) C = q. ( m ) (  T)

10. Specific Heat Practice The temperature of a 95.4g piece of copper increases from 25.0ᵒC to 48.0ᵒC when the copper absorbs 849J of heat. What is the specific heat of copper?

11. Example Problem Pg. 280 A 0.400 kg block of iron is heated from 295 K to 325 K. How much heat had to be transferred to the iron?

12. Calorimetry Calorimetry: used to measure heat flow into or out of a system Depends on the Law of Conservation of Energy E A + E B = 0  E A = -E B E = Q = m (C)  T E = Energy Q = amount of heat m = mass C = specific heat  T = change in the temperature

13. Example Problem Pg. 283 A calorimeter contains 0.50 kg of water at 15°C. A 0.040 kg block of zinc at 115°C is placed in the water. What is the final temperature of the system? (Specific heat of Zinc = 388 J/kg  ° C, Water = 4180 J/kg  ° C)

14. Section 12.2: Change of State and Laws of Thermodynamics

15. Change of State Latent heat = energy transferred during a phase change of a substance. – Heat of fusion (H f ): change liquid  solid OR solid  liquid – Heat of vaporization (H V ): change from a liquid  vapor OR vapor  liquid Q= mH f OR Q= mH V Q = Heat, m = mass and H = latent heat

19. Example Problem Pg. 288 You are asked to melt 0.100 kg of ice at its melting point and warm the resulting water to 20.0°C. How much heat is needed?

20. The First Law of Thermodynamics Thermal Energy can be increased by: – adding heat or – doing work SO: total increase in the thermal energy is the sum of the work done on it and the heat added to it. NOT FORBIDDEN BY FIRST LAW: – heat flow from cold to hot, – Heat engines convert energy with no waste & – random gas molecules do not organize themselves

21. Heat Engine A device able to convert thermal energy to mechanical energy. Requires High Temp. source and Low Temp. receptacle to deliver the thermal energy to, and a way to convert thermal energy into work. Example: Automobile Engines, Refrigerators and Heat Pumps

22. Automobile Combustion Engine

23. Efficiency Efficiency in a Carnot system (perfect engine) Efficiency = (1 – (T low /T high )) × 100

24. Efficiency Problem A heat engine operates between a high- temperature source and a low-temperature sink. It takes 500 J from the source and delivers 150 J to the sink. What is the efficiency of the heat engine?

25. The Second Law of Thermodynamics The “law of disorder” States: natural processes go in a direction that maintains or increases the total entropy of the universe. – Entropy = amount of disorder Basically ALL THINGS BECOME MORE DISORDERED (unless an action is taken to keep them ordered)

26. BeforeAfter

27. Entropy Calculation ΔS = Q/T ΔS = Change in entropy Q = Heat T = Temperature (in Kelvins)

28. Entropy Problem Calculate the entropy of 0.05 kg of ice at 0 °C. The heat of fusion of ice is 3.36×10 5 J/kg.