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Heat

Heat. Definitions Heat and Temperature Change Heat and Phase Change Mechanisms of Heat Flow Conduction Convection Radiation. Heat - Definitions. Energy transfer by non-mechanical means Transfer from hotter to colder Units calorie, kilocalorie. Cal - heat required to raise 1 g water 1°C

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Heat

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

  2. Heat - Definitions • Energy transfer by non-mechanical means • Transfer from hotter to colder • Units calorie, kilocalorie. • Cal - heat required to raise 1 g water 1°C • Kcal – heat required to raise 1 kg water 1°C • Calorie (food) • 1 kcal • Equivalent 1 cal = 4.186 J 1 kcal = 4.186 kJ • Mechanical equivalent – Friction - > Heat • Electrical equivalent – Electrical Energy - > Heat

  3. Heat – More Definitions • Internal Energy • Total energy contained (what’s in the account) • Heat • Non-mechanical input or output (credit/debit) • Work • Mechanical input or output (credit/debit) ΔU = Q - W • Internal Energy • U = ½ mv2 • U = 3/2NkT = 3/2nRT

  4. Specific Heat • Add heat to object, ΔT depends on • Quantity of Heat ( Q ) • Mass ( m ) • Material Property ( C ) Q = m C ΔT • SH is ability to absorb heat, distribute to molecules • Table 14-1 • Water, wood, etc • Why is water a coolant?

  5. Specific Heat Examples • Example 14-2 • Heat to heat iron vat • Heat with water • Example 14-3 (energy exchange example) • Hot pan, cold water • Pan cools more than water heats! • Qlost pan = Qgained water • Water has high specific heat!

  6. Calorimetry • Example 14-4 • Heat exchange problem • Heat lost tea = Heat gained cup • Set up equation, unknown final common Temperature • Example 14-5 • 1 Hot 2 cold • Determine SH

  7. Calorimetry Examples • Problem 11 (equilibrium – 1 hot 1 cold) • Problem 12 (equilibrium – 1 hot 2 cold) • Problem 13 • equilibrium – 1 hot 2 cold, find initial temperature • (HW) • Problem 14 • equilibrium – 1 hot 2 cold, find SH • (HW) • Problem 15 • Heat input – 2 cold • (HW)

  8. Specific and Latent Heat • Specific Heat Q = m C ΔT • Latent Heat Q = m L • Occurs during phase change • Ice - > liquid, liquid -> gas • No change in temperature • Depends on mass and L (Table 14.3 vs. 14.1)

  9. Latent Heat Examples • Example 14-7 (simple) • McDonald’s coffee with ½ inch ice • Example 14-8 • “Scenario analysis” • Cool water to 0C, raise ice to 0C • Melt all ice at 0C • Conclusion: all ice melts, rises above 0C • Solve problem • Other scenarios (double mass of ice)

  10. Other Latent Heat Examples • Example 14-9 • Solve for unknown latent heat

  11. Latent Heat Problems • Problem 24 • N2 is large so ice will reach 77 K • Problem 25 (repeat) • Problem 26 (iron boiler) • Problem 28 (steam and ice) • Problem 29 (repeat) • Problem 30 (kinetic energy melts ice)

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