1. In this chapter you will:  Learn how temperature relates to the potential and kinetic energies of atoms and molecules.  Distinguish heat from work.  Calculate heat transfer and the absorption of thermal energy.

2. Chapter 12 Sections Section 12.1: Temperature and Thermal Energy Section 12.2: Changes of State and the Laws of Thermodynamics

3. Section 12.1 Temperature and Thermal Energy Objectives Describe thermal energy and compare it to potential and kinetic energies. Distinguish temperature from thermal energy. Define specific heat and calculate heat transfer.

4. INTRODUCTION Energy – ability of an object to change itself or its surroundings. Thermodynamics – study of heat

5. THERMAL ENERGY Thermal Energy – the measure of the internal motion of an object’s particles. From Old Book Caloric – an invisible fluid added to a body when it was heated; this idea came from Scientists in the 18 th Century. This Caloric Theory could explain observations such as expansion when objects are heated, but it could not easily explain why hands warm up when rubbed together. In the Mid 19 th Century the caloric theory was replaced by Kinetic Molecular Theory. Kinetic Molecular Theory – this theory is based on the assumption that matter is made up of many tiny particles that are always in motion. In a hot body the particles move faster and thus have a higher energy than particles in a cooler body. Thermal Energy – is also called internal energy. It is the Sum of Kinetic Energy (KE) and Potential Energy (PE) of the internal motion of particles that make up an object.

6. THERMAL ENERGY AND TEMPERATURE Temperature only depends on the average Kinetic Energy of the particles in the object. The thermal energy in an object is proportional to the number of particles in it. Temperature, however, is not dependent on the number of particles in an object.

7. EQUILIBRIUM AND THERMOMETRY Conduction – transfer of kinetic energy when particles collide. It is most common in solids. It is the principle on which household thermometers work. Temperature – measure of hotness of an object on a quantitative scale. In gases it is proportional to the average kinetic energy of the particles. It does NOT depend on the number of particles in a body. Thermal Equilibrium – state in which the rate of energy flow between 2 or more bodies is equal and the objects are at the same temperature.

8. EQUILIBRIUM AND THERMOMETRY Thermometer – device used to measure temperature. It gets placed in contact with an object and allowed to come to thermal equilibrium with that object. The operation of a thermometer depends on some property such as volume that changes with temperature.

9. TEMPERATURE SCALES: CELSIUS AND KELVIN 3 Temperature Scales Fahrenheit (  F)(we use this on an every day basis in the US) Celsius (  C) Kelvin (K) The Celsius and Kelvin scales are usually used in science.

10. TEMPERATURE SCALES: CELSIUS AND KELVIN Figure 12-6 on p. 316 is helpful for conversions from one temperature scale to another. Temperature Scale Absolute Zero Water Freezes Body Temperature Water Boils Celsius -273  C0  C37  C100  C Kelvin0 K273 K310 K373 K Fahrenheit -459.4  F32  F98.6  F212  F

11. TEMPERATURE SCALES: CELSIUS AND KELVIN Equations to use to do temperature conversions. K =  C + 273  C = K – 273  C = (  F – 32) / 1.8  F =  C (1.8) + 32 or  C (9/5) + 32  F = (K – 273)(1.8) + 32 K = ((  F – 32) / 1.8) + 273

12. TEMPERATURE SCALES: CELSIUS AND KELVIN Numbers 5 and 6 are not really needed you can use the earlier equations as an intermediate step before you get the final answer. Generally materials contract as they cool and expand when they warm up. Hence the potholes in the winter time. Temperatures do not appear to have an upper limit but they do have a lower level. Absolute Zero – lowest possible temperature at which gas would have zero volume. Lowest temperature possible at this point all thermal energy would be removed from the gas. This temperature is at 0 K or –273  C. The Kelvin Temperature scale is based on Absolute Zero. Absolute Zero is at 0 K on the Kelvin Scale. Each interval on the Kelvin scale is equal to 1  C.

13. TEMPERATURE SCALES: CELSIUS AND KELVIN Kelvin – is the unit or interval on the Kelvin Scale. On the Celsius and Fahrenheit scale temperatures are in degrees. On the Kelvin Scale temperatures are in Kelvins. Example Problem  C to K K =  C + 273 = 25 + 273 = 298 K Example Problem K to  C  C = K – 273 = 4.22 – 273 = -268.78  C Do Practice Problems p. 317 # 1-2

14. HEAT AND THE FLOW OF THERMAL ENERGY One way to increase the temperature of an object is to place it in contact with a hotter object. Heat – energy that flows as a result of a difference in temperature. The symbol for heat is Q. Heat is a form of energy thus it is measured in Joules. It is the energy transferred because of a difference in temperature. If Q is negative that means it lost heat and if Q is positive that means it absorbed energy. Thermal Energy is transferred in 3 ways Conduction Convection Radiation

15. HEAT AND THE FLOW OF THERMAL ENERGY Conduction – it involves the transfer of kinetic energy when the particles of an object collide. It is most common in solids. It is the principle on which household thermometers work. Convection – heat transfer by means of motion of fluid. Convection currents in the atmosphere are responsible for much of earth’s weather. Both Conduction and Convection depend on the presence of Matter. Radiation – electromagnetic waves that carry energy. It does not depend on the presence of matter. Thermal energy can be transferred through space in the form of electromagnetic waves, such as solar energy transmitted to the Earth.

16. SPECIFIC HEAT Specific Heat – the amount of energy that must be added to raise the temperature of a unit mass one temperature unit. The symbol for specific heat is C. It is measured in Joules per kg Kelvin (J / kg*K). Table 12.1 p. 318 gives a list of Common Specific Heats The Heat Gained or Lost by an object as its temperature changes depends on the mass, the change in temperature and the specific heat of the substance. Heat Transfer – is equal to the mass of an object times the specific heat of the object times the difference between the final and initial temperatures.

17. SPECIFIC HEAT To find the heat gained or lost by an object we use the equation Q = mC  T Heat Gained or lost (Q) = the mass (m) times by the specific heat (C) times by the change in temperature (  T). We can calculate ΔT in Kelvins or in °C. Do Example 1 p. 318 Q = mCΔT Q = (5.1)(450)(450 – 295) Q = (5.1)(450)(155) Q = 355,725 Joules Do Practice Problems p. 319 # 3-5

18. CALORIMETRY: MEASURING SPECIFIC HEAT Calorimeter – device that isolates objects to measure temperature changes due to heat flow. It is a device used to measure changes in thermal energy. It depends on the conservation of energy in a closed, isolated system. As a result of the isolation, if the energy of one part of the system increases, the energy of another part must decrease by the same amount. Conservation of Energy – in a Closed, Isolated System, the thermal energy of object A plus the thermal energy of object B is Constant. E A + E B = constant  E A +  E B = 0

19. CALORIMETRY: MEASURING SPECIFIC HEAT If the thermal energy change is positive the temperature of that block rises. If the thermal energy change is negative the temperature of that block falls. Heat will flow from the hotter object to the colder object until the objects reach thermal equilibrium (Have same temperature). The change in thermal energy is equal to the heat transferred:  E = Q = mC  T Increase of thermal energy of Block A is equal to the decrease in thermal energy of Block B, thus we have m A C A  T A + m B C B  T B = 0

20. CALORIMETRY: MEASURING SPECIFIC HEAT The final Temperature of the 2 blocks are equal thus the equation for the Transfer of Energy is m A C A (T F – T AI ) + m B C B (T F - T BI ) = 0 Do Example Problem 2 p. 251 321 m A C A (T F – T AI ) + m B C B (T F - T BI ) = 0.04(388)(T F – 115) +.5(4180)(T F – 15) = 0 15.52 T F – 1,784.8 + 2,090 T F – 31,350 = 0 2,105.52 T F = 33,134.8 T F = 15.74  C Do Practice Problems p. 321 # 6-9 Do 12. 1 Section Review p. 322 # 10-18