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Chapter 6 Notes HEAT

Chapter 6 Notes HEAT. Heat & Temperature Calculations. Temperature = a measure of the AVERAGE kinetic energy in the substance. Celsius (°C) Fahrenheit (°F) Kelvin (°K). 0°K = absolute zero = all molecular motion stops. H 2 0 distilled water (pure water). melting point = 0°C

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Chapter 6 Notes HEAT

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  1. Chapter 6 NotesHEAT Heat & Temperature Calculations

  2. Temperature= a measure of the AVERAGE kinetic energy in the substance. • Celsius (°C) • Fahrenheit (°F) • Kelvin (°K)

  3. 0°K=absolute zero = all molecular motion stops

  4. H20 distilled water (pure water) • melting point = 0°C • boiling point = 100°C

  5. Melting Points examples Gallium a# 31 M.P. 86oF Iron a# 26 M.P. 2800oF Mercury a# 80 M.P. -38oF Gold a# 79 M.P. 1947oF Copper a# 29 M.P. 1984oF

  6. Boiling Pointsexamples Gallium a# 31 B.P. 3999oF Iron a# 26 B.P. 5182oF Mercury a# 80 B.P. 674oF Gold a# 79 B.P. 5173oF Copper a# 29 B.P. 4644oF

  7. Energy (heat) measure in Joules, BTUs (British Thermal Units) calories and Calories. • 1 calories = 4.186 Joules • 1 BTU = 252 calories • 1 Calorie = 1000 calories

  8. States of Matter • Also called Phases of Matter • Solids • Liquids • Vapors (gases)

  9. Solids • Have a definite shape • Have a definite volume • Particles VIBRATE in place

  10. Liquids • Have NO definite shape • Have definite volume • particles SLIDE freely

  11. Gases (vapor) • Have NO definite shape • Have NO definite volume • particles fill the volume of the container

  12. Solids, Liquids & Gases • Solids = can form crystals = solid where the particle are arranged into repeating patterns. • Liquids = physical property of Viscosity = “thickness” – the resistance to flow. • Gases = volume of gases depend greatly on pressure and temperature.

  13. Phase Changes • Melting • Freezing • Vaporization • Condensation • Sublimation • physical changes

  14. Melting • the process of changing from a solid to a liquid • energy is being put into the substance • melting point = the temperature at which melting occurs – physical property • the melting point of water is 0ºC

  15. Freezing • the process of changing from a liquid to a solid • energy is being pulled out of the substance • freezing point =same temperature as the melting point • (used mainly in weather)

  16. Vaporization • the process of changing from a liquid to a gas • energy in being put into the substance • evaporation • boiling

  17. Evaporation • vaporization that occurs at the surface of the liquid

  18. Boiling • vaporization that occurs throughout the liquid • boiling point= the temperature at which boiling occurs • the boiling point of water is 100ºC

  19. Condensation • the process of changing from a gas to a liquid • energy is being pulled out of the substance

  20. Sublimation • the process of changing from a solid to a gas • energy is being put into the substance • ex: dry ice (CO2)

  21. Heating of water STEAM 100°C WATER (liquid) heat of vaporization 0°C ICE heat of fusion

  22. Heat Transfer • Conduction • Convection • Radiation

  23. Conduction • transfer of heat by direct contact (molecule to molecule) • metals are good conductors • poor conductors = insulators

  24. Convection • transfer of heat by “convection currents” warm fluids are less dense than colder fluid thus warm fluids rise and cold fall. • not possible in solids • fluid = anything that flows (liquids & gases) • hot air balloons, “convection” ovens

  25. Radiation • transfer of heat by electromagnetic waves • some wavelengths of infrared & ultraviolet • only type of transfer that can occur through empty space • sun  Earth

  26. Specific Heat The amount of heat needed to raise the temperature of one gram of a substance one degree Celsius.

  27. types of substance (C) mass of the substance (m) how much of a temperature change (∆T) C = specific heat constant m = mass ∆T = difference in the temperature Factors in Specific Heat

  28. Specific Heat Calculations • ∆Q = amount of heat absorbed (difference in the heat or heat change) • ∆Q = m x ∆T x C • The specific heat of water • = 1.0 cal/g°C or • = 4.2 joules/ g°C

  29. C = 1.0 cal/g°C m = 500 grams ∆T = 10°C (30-20) ∆Q = m x ∆T x C ∆Q = (500 g)(10°C)(1.0 cal/g°C) ∆Q = 5000 calories EXAMPLE #1:How many calories are absorbed by a pot of water with a mass of 500 grams in order to raise the temperature from 20°C to 30°C?

  30. C = 4.2 J/g°C m = 500 grams ∆T = 10°C (30-20) ∆Q = m x ∆T x C ∆Q = (500 g)(10°C)(4.2 J/g°C) ∆Q = 21,000 Joules EXAMPLE #2:How many joules are absorbed by a pot of water with a mass of 500 grams in order to raise the temperature from 20°C to 30°C?

  31. Phase Changes • Heat of fusion (Hf) • the heat energy needed to melt (or freeze) a substance. • All heat being put into the substance goes to the melting process • thus the temperature does not change while the substance is melting.

  32. Phase Changes • Heat of vaporization (Hv) • the heat energy needed to boil (or condense) a substance. • All heat being put into the substance goes to the boiling process • thus the temperature does not change while the substance is boiling.

  33. Heat & Phase Changes • Hf = mass x Hf constant • The heat of fusion of water = 340 J/g • Hv = mass x Hv constant • The heat of vaporization of water = 2300 J/g

  34. EXAMPLE:How many joules of heat are necessary to melt 500 g of ice? • Chf = 340 J/g • m = 500 g • H = Chf x m • H = (340 J/g)(500 g) • H = 170,000 J

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