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Heat

Heat. Lab 31 Terms. Δ (delta) means change Subtract FINAL – INITIAL. Temperature = average kinetic energy of particles in a substance Measured with a thermometer. Q means HEAT measured in calories or Joules ΔQ means change in heat. HEAT

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Heat

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  1. Heat

  2. Lab 31 Terms • Δ (delta) means change • Subtract FINAL – INITIAL • Temperature = average kinetic energy of particles in a substance • Measured with a thermometer

  3. Q means HEAT measured in calories or Joules • ΔQ means change in heat. • HEAT The flow of thermal energy from HIGH to LOW temperature Must be calculated

  4. calorie = amount of heat required to raise the temperature of 1 g of water 1oC • 1 calorie = 4.18 Joules

  5. Calorimeter Styrofoam cup calorimeter an insulated container where a reaction can be performed and heat can be calculated http://www.chem.purdue.edu/gchelp/howtosolveit/Thermodynamics/ThermoArt/Calorimeter.JPG

  6. Flip page over to II. Heat EquationΔQ = m · c · ΔT Heat = mass x heat capacity x change in temp cal = g X X ºC c for water = 1 density of H2O = 1 g/ml • Find by taking T2 – T1

  7. m T1 T2 ? 1 Try this: 100 ml of water warms from 10 ºC to 30 ºC. What is the heat gained? m = ΔT = c = ΔQ = m · c · ΔT ΔQ = 100g · 1 · (20 ºC) ΔQ = 2000 cal 100 g 30oC – 10oC = 20oC

  8. m T1 T2 ? Lab 31 Pre Lab Questions If 10.00 g of water is changed from 70ºC to 85ºC. What is the ΔQ (change in heat)? ΔQ = m · c · ΔT ΔQ = 10g · 1 · (85 ºC - 70 ºC) ΔQ = 150 cal

  9. Lab 31 Pre Lab Questions 300 calories of heat is added to 100 ml of water at 20 ºC. • What is the mass of water? 100g • What is the ΔT of the water? • What would the final temperature be? 23o C ΔQ = m · c · ΔT300 cal = 100g · 1 · ΔT ΔT = 3o C

  10. m = ? T2 ∆Q T1 1 cal g Lab 31 Pre Lab Questions • What mass of water is in a calorimeter if it takes 1500 calories to heat it from 10 ºC to 65 ºC? DQ = m c DT 1500 cal = m · 1 · (65 ºC - 10 ºC) m = 27.27 g

  11. cal g http://www.skthew.com/upload/image/time_ice_melting.jpg Heat of Fusion heat needed to melt 1 g of a solid. Heat of Fusion = For ice, Heat of Fusion = 80

  12. Lab 32 Terms Law of Conservation of Energy = Energy is neither created nor destroyed…Only Transferred. Heat Lost = Heat Gained

  13. http://www2.uni-siegen.de/~pci/versuche/pics/exo4.jpg http://www.photospin.com/content/photos/thumb/PS012046.jpg • Exothermic = a reaction that releases heat…Feels HOT! Temp Rises • Endothermic = a reaction that absorbs heat…Feels COOL! Temp Decreases

  14. Lab 32: Heat of Crystallization Heat is released Heat

  15. 65 35.1 cal cal g g Heat of Crystallization Heat of Crystallization Heat released as 1 g of a substance crystallizes. For wax = For napthalene =

  16. Lab 33: Specific Heat Capacity • Symbol: c • heat needed to raise 1 g of substance 1oC • Units: • cwater = 1 • cAl = 0.21 • cCu = 0.09 • cFe = 0.11

  17. 2 L H2O at 50º C 2 L H2O at 90º C Review:Which is holding more heat?

  18. 10 L H2O at 50º C 2 L H2O at 50º C Examples:Which is holding more heat?

  19. 2 kg gold at 50º C 2 kg H2O at 50º C Examples:Which is holding more heat?

  20. Lab 34 • “Error of the Air” assuming room temp is about 20 ºC by starting our experiments at 10 ºC and finishing at 30 ºC we can limit the error from heat gained from the room or lost to the room. finish 30oC 20oC 10oC start

  21. 33,000 7,000 Joules cal g g Heat of Combustion Heat of Combustion Heat released as 1 g of a substance burns. For candle = For nut = Remember, 1 cal = 4.18 J

  22. Temperature Scales

  23. Cooling Curve Heat of fusion Heat of crystallization Heat of combustion DQ = mcDT g g  l DQ = mcDT temperature l l s DQ = mcDT s time

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