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Chapter 16

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  1. Chapter 16 Thermal Energy and Heat

  2. Section 16-1 Thermal Energy and Matter

  3. Work and Heat • Heat is the transfer of thermal energy from one object to another because of a temperature difference. • Heat flows spontaneously from hot objects to cold objects.

  4. Temperature • Temperature is a measure of how hot or cold an object is compared to a reference point. • On the Celsius scale, the reference points are the freezing and boiling points of water. • On the Kelvin scale, another reference point is absolute zero (0 K).

  5. Temperature • Temperature is related to the average kinetic energy of the particles in an object due to their random motions through space. • Remember the kinetic theory!!

  6. Thermal Energy • Thermal energy depends on the mass, temperature, and phase (solid, liquid, or gas) of an object. • There is more thermal energy in a teapot full of hot water than there is a tea cup of the same temperature water…because there is more mass to the water in the teapot.

  7. Thermal Contraction and Expansion • Thermal expansion is an increase in the volume of a material due to a temperature increase. • Thermal expansion occurs when particles of matter move farther apart as temperature increases.

  8. Specific Heat • Specific heat is the amount of heat needed to raise the temperature of one gram of a material by one degree Celsius. • The lower a material’s specific heat, the more its temperature rises when a given amount of energy is absorbed by a given mass.

  9. Specific Heat Q = m x c x ∆T

  10. Measuring Heat Changes • A calorimeter is an instrument used to measure changes in thermal energy. • A calorimeter uses the principle that heat flows from a hotter object to a colder object until both reach the same temperature.

  11. Section 16-2 • Heat and Thermodynamics

  12. Conduction • Conduction is the transfer of thermal energy with no overall transfer of matter. • Conduction in gases is slower than in liquids and solids because the particles in a gas collide less often.

  13. Conduction • Thermal conductor is a material that conducts thermal energy well. Can you think of any???? • Thermal insulator is a material that conducts thermal energy poorly. What are some examples?????

  14. Convection • Convection is the transfer of thermal energy when particles of a fluid move from one place to another. • Convection current occurs when a fluid circulates in a loop as it alternately heats up and cools down.

  15. Convection • Convection currents are important in many natural cycles, such as ocean currents, weather systems, and movements of hot rock in Earth’s interior.

  16. Radiation • Radiation is the transfer of energy by waves moving through space. • Heat lamps used in restaurants are a familiar example of radiation. • All objects radiate energy. As an object’s temperature increases, the rate at which it radiates energy increases.

  17. Thermodynamics • The study of conversions between thermal energy and other forms of energy is called thermodynamics.

  18. Laws of Thermodynamics • The first law of thermodynamics states that energy is conserved. • The second law of thermodynamics states that thermal energy can flow from colder objects to hotter objects only if work is done on the system. • The third law of thermodynamics states that absolute zero cannot be reached.

  19. Thermodynamics • A heat engine is any device that converts heat into work • Thermal energy that is not converted into work is called waste heat. • The efficiency of heat engines is always less than 100%. There is always some heat that is wasted.

  20. Section 16-3 • Using Heat

  21. Heat Engines • The two main types of heat engines are the external combustion engine and the internal combustion engine.

  22. Heat Engines • External combustion engine – an engine that burns fuel outside the engine. • Internal combustion engine – a heat engine that burns fuel inside the engine

  23. Heating Systems • Central heating systems heat many rooms from one central location. • Most heating systems use convection to distribute thermal energy.

  24. Types of Heating • Hot water heating - boiler heats water that is pumped to radiators in each room. • Steam heating – like hot water, but steam is used. • Electric baseboard heating – uses electrical energy to heat a room. • Forced-air heating – uses fans to circulate hot air through ducts to the rooms.

  25. Cooling Systems • Most cooling systems are heat pumps. • Heat pump – reverses the normal flow of thermal energy. They circulate a refrigerant through tubing. • Refrigerant is a fluid that vaporizes and condenses inside the tubing of a heat pump.

  26. Heat Pumps • Heat pumps must do work on a refrigerant in order to reverse the normal flow of thermal energy.

  27. Refrigerators & AC • A refrigerator is a heat pump - it transfers thermal energy from the cold food compartment to the warm room. • Air conditioners – 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.