Chapter 16 THERMAL ENERGY AND HEAT Chapter 16.1 Thermal Energy and Matter Introduction 1. What did most scientists thought about heat in the 1700s? Scientists thought heat was a fluid called caloric. It would flowed between objects. Chapter 16 Thermal Energy and Matter Benjamin Thompson Count Rumford 2. Who was Count Rumford? American-born scientist (1753-1814) 3. What concept did he challenged? The Concept of heat. 4. How did he do this? Chapter 16.1 Thermal Energy and Matter A brass cylinder is drilled to make a cannon barrel. Water is used to cool the brass so that it did not melt. Rumford observed that the brass became hot as long as the drilling continued, producing enough heat to boil the water. Soon after the drilling stopped, however, the water stopped boiling Chapter 16.1 Thermal Energy and Matter A. Work and Heat 1. Summary A drill is a machine that does work on the cannon. The more work done by the drill, the more that friction causes the cannon to heat up. 2. What is Heat? It is the transfer of thermal energy from one object to another because of a temperature difference. Chapter 16.1 Thermal Energy and matter B. Temperature 3. What is temperature? It is a measure of how hot or cold an object is compared to a reference point. 4. What is the relationship between temperature, speed of the particles, and average kinetic energy? As the temperature increases, speed of the particle increases, average kinetic energy increases. Chapter 16.1 Thermal Energy and Matter C. Thermal Energy 5. Recall that thermal energy is the total potential and kinetic energy of all the particles in an object 6. What does thermal energy depend on? Mass Temperature Phase of the object Chapter 16.1 Thermal Energy and Matter D. Thermal Contraction and Expansion 7. What is thermal expansion? It is an increase in the volume of a material due to a temperature increase. 8. Why does this occur? It occurs when particles of matter move farther apart as temperature increases. Chapter 16.1 Thermal Energy and Matter D. Thermal contraction and expansion 9. What is thermal contraction? It is a decrease in the volume of a material due to a temperature decrease. 10. Why does this occurs? It occurs when particles of matter move closer together as temperature decrease. Chapter 16.1 Thermal Energy and Matter E. Specific Heat 11. What is Specific Heat? It is the amount of heat needed to raise the temperature of one gram of a material by one degree Celsius. 12. What is the relationship between specific heat and temperature? The lower a material’s specific heat, the more its temperature rises when a given amount of energy is absorbed by a given mass. Chapter 16.1 Thermal Energy and Matter E. Specific Heat 13. What is the formula for specific heat? Q = m x c x ∆T Specific Heats of Selected Materials Material (at 100 kPa) Specific Heat (j/g•C°) Water 4.18 Plastic 1.84--2.09 Air 1.01 Iron 0.449 Silver 0.235 Chapter 16.1 Thermal Energy and Matter Name Symbol Unit Equation Heat Q Joules Q = m x c x ∆T Mass M Grams M = Q / (c x ∆T) Specific heat C j/g•C° C = Q / (m x ∆T) Change in Temperature ∆T C° ∆T = Q / (m x c) Chapter 16.1 Thermal Energy and Matter Page 477 Math Skills, Calculating Specific Heat List, formula, sub and answer 21, 375 joules Page 477 Math Practice 1. 35.5 kJ 2. 34 kJ 3. 3.8 C° 4. 10.0 C° 5. 42 g Chapter 16.1 Thermal Energy and Matter F. Measuring Heat Changes 14. What is calorimeter? It is an instrument used to measure changes in thermal energy. 15. What principle does the calorimeter use? Heat flows from a hotter object to a colder object until both reach the same temperature. Chapter 16.1 Thermal Energy and Matter F. Measuring Heat Changes 16. Why does this principle work? According to the law of conservation for energy, the thermal energy released by a test sample is equal to the thermal energy absorbed by its surroundings. Page 478 Math Practice Problems 10 & 11 10. 7800 joules 11. 43.5 C° Chapter 16.2 Heat and Thermodynamics Introduction What are the three ways to transfer heat? Conduction Convection Radiation 1. Chapter 16.2 Heat and Thermodynamics A. Conduction What is conduction? It is the transfer of thermal energy with no overall transfer of matter It occurs within a material or between materials that are touching. 1. 2. What is the rate of conduction in the phases of matter? In general, conduction occurs faster in solids, than liquid, than in gases. Chapter 16.2 heat and Thermodynamics A. Conduction 3. What are the types of materials used in conduction? Thermal conductor is a material that transfers thermal energy well. Metals are example. Thermal Insulator is a material that does not transfer thermal energy well. Wood and glass are examples. Chapter 16.2 heat and Thermodynamics Chapter 16.2 Heat and Thermodynamics B. Convection 4. What is convection? It is the transfer of thermal energy when particles of a fluid move from one place to another. 5. What is a convection current? It occurs when a fluid circulates in a loop as it alternately heats up and cools down. Chapter 16.2 Heat and Thermodynamics Chapter 16.2 Heat and Thermodynamics C. Radiation 6. What is radiation? It is the transfer of energy by waves moving through space. 7. What is the relationship between temperature and radiate energy? As an object’s temperature increases, the rate at which it radiates energy increases. Chapter 16.2 Heat and Thermodynamics Chapter 16.2 Heat and Thermodynamics D. Thermodynamics 8. What is thermodynamics? It is the study of conversions between thermal energy and other forms of energy. Chapter 16.2 Heat and Thermodynamics D. thermodynamics 9. What did James Prescott Joule do? He carefully measured the energy changes in a system. He found that the work done almost exactly equaled the thermal energy gained by the water. Chapter 16.2 Heat and Thermodynamics D. Thermodynamics 10. What are the laws of Thermodynamics? 1st Law of Thermodynamics Energy is conserved. Chapter 16.2 Heat and Thermodynamics D. Thermodynamics 2nd Law of Thermodynamics Thermal energy can flow from colder objects to hotter objects only if work is done on the system. Chapter 16.2 Heat and Thermodynamics D. Thermodynamics 3rd Thermodynamics Absolute zero cannot be reached. Chapter 16.3 Using Heat A. Heat Engines What is a heat engine? It is a system that performs the conversion of heat or thermal energy to Mechanical work. 1. Chapter 16.3 Using Heat A. Heat Engines 2. What are the types of heat engines? External combustion Internal combustion Chapter 16.3 Using Heat A. Heat Engines 3. What is an external combustion engine? It is an engine that burns fuel outside the engine. 4. What is an example? A Steam engine. Chapter 16.3 Using Heat A. Heat Engines 5. What is an internal combustion engine? It is a heat engine in which the fuel burns inside the engine. 6. What is an example? Most cars use them. Chapter 16.3 Using Heat 7. Describe the sequence of events in one cylinder of a four-stroke engine. Chapter 16.3 Using Heat B. Heating Systems 8. What was the principal method of heating buildings at the start of the industrial revolution? Wood-burning fireplaces Chapter 16.3 Using Heat B. Heating Systems 9. What type of heating system is used today? Central heating system which heats many rooms from one central location usually found in the basement. Chapter 16.3 Using heat B. Heating Systems 10. What are the different types of heating systems? Hot-Water Heating Steam Heating Electric Baseboard Heating Forced-Air Heating Chapter 16.3 Using Heat B. Heating Systems Hot-Water Heating System Within the pipes of a hotwater heating system, the water circulates in a convection current. In each room, the air moves in a convection current. Chapter 16.3 Using Heat B. Heating Systems Steam Heating System very similar to hot-water heating except that steam is used instead of hot water. Chapter 16.3 Using Heat B. Heating Systems Electric Baseboard Heating System The hot coil heats the air near it by conduction and radiation. Then convection circulates the warm air to heat the room. Chapter 16.3 Using Heat B. Heating Systems Forced-Air Heating System The hot air enters the room through a supply vent in the floor. The hot air rises as cooler, denser air in the room sinks. The cooler air returns to the furnace through the return vent. Chapter 16.3 Using Heat C. Cooling Systems 11. What is a cooling system? A system that takes heat from one area to another. Chapter 16.3 Using Heat C. Cooling Systems 12. What is a heat pump? It is a device that reverses the normal flow of thermal energy. 13. What is a refrigerant? It is a fluid that vaporizes and condenses inside the tubing of a heat pump. Chapter 16.3 Using Heat C. Cooling systems 14. Important statements Thermal energy flows spontaneously from hot to cold objects. Heat pumps must do work on a refrigerant in order to reverse the normal flow of thermal energy. Chapter 16.3 Using Heat C. Cooling systems 15. What are refrigerators? It is a heat pump that transfers thermal energy from the cold food compartment to the warm room. Chapter 16.3 Using Heat C. Cooling systems 16. What are air conditioners? A device used to cool the air in your home. Outside air is heated as a fan blows it through the condenser coil. Inside the room, a fan draws in warm air through the evaporator coil. The fan blows cooled air out into the room.