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Heat and Temperature Change

Heat and Temperature Change. Definitions Heat and Temperature Change Examples Heat and Phase Change Examples Mechanisms of Heat Flow Conduction Convection Radiation. Heat - Definition. Energy Transfer by non-mechanical means Heating water on stove (chemical/electrical)

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Heat and Temperature Change

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  1. Heat and Temperature Change • Definitions • Heat and Temperature Change • Examples • Heat and Phase Change • Examples • Mechanisms of Heat Flow • Conduction • Convection • Radiation

  2. Heat - Definition • Energy Transfer by non-mechanical means • Heating water on stove (chemical/electrical) • Burning gasoline in engine (chemical) • Touching a hot/cold object (conduction) • Losing heat through glass window (conduction) • Feeling heat from sun (electromagnetic) • Heating food in microwave (electromagnetic) • Each involves energy transfer by non-mechanical means and raising/lowering of temperature • Heat flows from “hot” to “cold”

  3. Heat - Definitions • Units of Heat. • Calorie - heat required to raise 1 g water 1°C • Kilocalorie - 1000 calories • Calorie (food) • Actually uses kilocalories • Heat given off by incinerating • Mechanical Equivalent • 1 cal = 4.186 J 1 kcal = 4.186 kJ • Mechanical equivalent – Friction - > Heat • Electrical equivalent – Electrical Energy - > Heat

  4. Heat and Internal Energy • Internal Energy • Total thermal energy contained. • Heat • Non-mechanical input or output Q U U Q

  5. Heat and Temperature Change • Adding heat to object causes temperature change. Q – Quantity of Heat (J) (cal) m – Mass (kg) c – Specific Heat ( J/kg C°) ΔT – Temperature change (C°)

  6. Specific Heat and Temperature Change • Specific Heat measures ability to absorb heat and distribute to molecules. • Table 14-1 • Water, wood, etc • Why is water a coolant?

  7. Example 14-2 • (a) How much heat is required to raise the temperature of an empty 20 kg vat made of iron from 10°C to 90°C? (b) What if the vat is filled with 20 kg water? • Empty • Filled with 20 kg water

  8. Example 14-3 – Hot pan in the sink - 1 • 5 kg skillet at 200°C placed in sink with 40x50x10 cm water at 20°C. What is final temperature? • Mass of water • Requirement for equilibrium • Heat lost by skillet = heat gained by water. • Final temperature same. • Heat exchange equation: Heat lost by skillet = heat gained by water. Now just solve..

  9. Example 14-3 – Hot pan in the sink - 2 • 5 kg skillet at 200°C placed in sink with 20 kg water at 20°C. What is final temperature? • Heat exchange equation • Fill in (make each temperature change positive) Pan cools more than water heats!

  10. Example 14-4 – Cup cools tea. • Heat exchange equation: Heat lost by tea = heat gained by cup. • Fill in (make temperature changes positive) Again the water (tea) dominates

  11. Example 14-5 – 1 hot, 2 cold • Wanted to know specific heat of alloy. 0.150 kg sample heated to 540°C, transferred to 400 g water contained in 200 g aluminum calorimeter cup, all at 10.0°C. Finally temperature observed at 30.5°C. • Heat exchange equation: (assume water and cup same ΔT)

  12. Problem 11 – cold thermometer in hot water • Heat exchange equation: Heat lost by water = heat gained by thermometer • Fill in numbers:

  13. Problem 12 – hot copper in water + cup • Heat exchange equation: (assume water and cup same ΔT) Heat lost by copper = heat gained by water + heat gained by cup • Fill in numbers:

  14. Problem 13 - hot iron in water + vat • Heat exchange equation: (assume water and vat same ΔT) Heat lost by horseshoe = heat gained by water + heat gained by vat • Fill in numbers:

  15. Problem 15 • Heat required to heat both coffee and pot • How long to supply 318,642 J at 750 J/s (watts)

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