Chapter 16 Heat 1

What is Heat Heat is the transfer of thermal energy from one object to another because of a temperature difference. Heat is the transfer of thermal energy from one object to another because of a temperature difference. Most objects expand when exposed to heat Most objects expand when exposed to heat Flows from hot objects to cold objects Flows from hot objects to cold objects 2

What is Temperature Is a measure of how hot or cold an object is compared to a reference point. Is a measure of how hot or cold an object is compared to a reference point. As temperature increases, the particles move faster As temperature increases, the particles move faster Instrument: THERMOMETER Instrument: THERMOMETER –Measures thermal expansion 3

Thermal Energy Total potential and Kinetic energy of all the particles in an object. Total potential and Kinetic energy of all the particles in an object. Depends on the mass, temperature and phase of an object. Depends on the mass, temperature and phase of an object. 4 As temperature rises, thermal energy rises too.

Specific Heat The amount of heat needed to raise the temperature of one gram of a material by one degree Celsius. 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 The lower a material’s specific heat, the more its temperature rises when a given amount of energy is absorbed by a given mass Measured in Joules per gram per degree Celsius Measured in Joules per gram per degree Celsius –J/g*ºC Formula Formula Q=m*c*ΔT Q=heat absorbed (unit=J) Q=heat absorbed (unit=J) m=mass (unit=g) m=mass (unit=g) c=specific heat c=specific heat ΔT=change in temperature ΔT=change in temperature 5

Heat of ______ of water Vaporization The heat required to boil Liquid to gas 340 J/g Fusion The heat required for melting Solid to liquid 2300 J/g

Calorimeter An instrument used to measure changes in thermal energy An instrument used to measure changes in thermal energy Uses the principle that heat flows from a hotter object to a colder object until both reach the same temperature Uses the principle that heat flows from a hotter object to a colder object until both reach the same temperature 7

Kelvin Scale Starts at 0 and goes up. (all positive numbers) Starts at 0 and goes up. (all positive numbers) Absolute Zero  0 K Absolute Zero  0 K  No movement of atoms or molecules Convert ºC to K Convert ºC to K  K=ºC Practice Practice 73ºC= ________ K 73ºC= ________ K -50ºC= ________K -50ºC= ________K 250K= ________ºC 250K= ________ºC 500K= ________ºC 500K= ________ºC 8

Conduction The transfer of thermal energy with no overall transfer of matter. The transfer of thermal energy with no overall transfer of matter. Objects are touching Objects are touching Conduction in gases is slower than in liquids and solids because the particles in a gas collide less often. Conduction in gases is slower than in liquids and solids because the particles in a gas collide less often. EX: Touching a hot metal spoon EX: Touching a hot metal spoon 9

Convection Transfer of thermal energy when particles of a fluid move from one place to another. Transfer of thermal energy when particles of a fluid move from one place to another. Usually in liquids and gases because they flow easy Usually in liquids and gases because they flow easy Ex: boiling water Ex: boiling water 10

Radiation Transfer of energy by waves moving through space. Transfer of energy by waves moving through space. All objects radiate energy All objects radiate energy As an object’s temperature increases, the rate at which it radiates energy increase As an object’s temperature increases, the rate at which it radiates energy increase Ex: The Sun Ex: The Sun 11

Conductors vs. Insulators Conductors Materials that conducts thermal energy well. Materials that conducts thermal energy well. Ex: Ex: –wire rack in an oven –Pots and pans Insulators A material that conducts thermal energy poorly. A material that conducts thermal energy poorly. Ex: Ex: –Wooden spoon –Air 12

Thermodynamics The study of conversions between thermal energy and other forms of energy The study of conversions between thermal energy and other forms of energy Law 1 Law 1 –Energy is neither created nor destroyed Law 2 Law 2 –Thermal energy can flow from colder objects to hotter objects but is transfer to other items Law 3 Law 3 –Absolute zero cannot be reached on Earth. 13