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Heat

Heat. Objectives Be able to distinguish between heat and temperature Be able to explain thermal equilibrium Identify the three ways heat can be transferred Understand specific heat and latent heat. What is Temperature?. Temperature is our measurement of the average

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Heat

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  1. Heat • Objectives • Be able to distinguish between heat and temperature • Be able to explain thermal equilibrium • Identify the three ways heat can be transferred • Understand specific heat and latent heat

  2. What is Temperature? Temperature is our measurement of the average kinetic energyfound in the random motions and vibrations of countless atoms and molecules. Temperature is a way of quantifying the kinetic energy of these atoms and molecules. Temperature is Energy.

  3. Maxwell-Boltzman Velocity Distribution Higher temperatures mean higher velocities for atoms and molecules

  4. Heat Transfer Three Modes of Heat Transfer Radiation Convection Conduction

  5. Radiation Energy transport via electromagnetic waves

  6. Convection Energy transport by mass motion

  7. Conduction Energy transport by vibrational translation The jostling of atoms and molecules in close proximity in a solid, especially one with high conductivity.

  8. Specific Heat • Q = m c DT Q = HEAT ENERGY m = mass DT = Temperature difference c = specific heat responsible for the thermal properties of the substance (Joules/kg/Celsius) DT = Q/mc

  9. Specific Heat DT = Q/mc For a given amount of heat energy, say 10,000 Joules, what is the temperature change for 1 kg of water and 1 kg of sand? Csand = 838 J/kgoC Cwater = 4186 J/kgoC DTsand = 10,000/1(838) = 11.9 oC DTwater = 10,000/1(4186) = 2.4 oC

  10. Heat Energy

  11. Changes of State Energy Increased and Absorbed by Substance: • SOLID to LIQUID Melting • LIQUID to GAS Boiling • SOLID to GAS Sublimation Energy Decreased and Released by Substance: • GAS to SOLID Deposition • GAS to LIQUID Condensation • LIQUID to SOLID Freezing

  12. Latent Heat

  13. Latent Heat of Fusion Heat Energy required to convert solid to liquid Lf

  14. Latent Heat of Vaporization Heat Energy required to convert liquid to gas. Lv

  15. Melting DT = Q/mc Amount of heat energy needed to bring a 25 g ice block to a temperature of 50oC? Starting Temp = 0oC Ending Temp = 50oC Q = heat needed to make transition from ice to water + heat needed to heat water from 0 to 50 oC Q= mLf + mcDT

  16. Melting Ice Q = m Lf + m c DT Q = heat needed to make transition from ice to water + heat needed to heat water from 0 to 50 oC = 80 cal/g*(25 g)*(4.186 J/1000 Cal) +25 g *4.186 J/goC *(50-0 oC) = 8.37 J + 5230 J = 5238.4 J

  17. Temperature Conversions CELCIUS C = 5/9 (F-32) FAHRENHEIT F = (9/5 C) + 32 ABSOLUTE or KELVIN K = C + 273

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