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What happens to thermal (heat) energy?

What happens to thermal (heat) energy?. When objects of different temperature meet: Warmer object cools Cooler object warms Thermal energy is transferred q warmer = -q cooler specific heat x mass x T = specific heat x mass x T warmer object cooler object.

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What happens to thermal (heat) energy?

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  1. What happens to thermal (heat) energy? • When objects of different temperature meet: • Warmer object cools • Cooler object warms • Thermal energy is transferred • qwarmer = -qcooler • specific heat x mass xT = specific heat x mass xT • warmer object cooler object

  2. Heat transfer between substances:

  3. Thermal Energy and Phase Changes First: What happens?

  4. But what’s really happening? • Warming: • Molecules move more rapidly • Kinetic Energy increases • Temperature increases • Melting/Boiling: • Molecules do NOT move more rapidly • Temperature remains constant • Intermolecular bonds are broken • Chemical potential energy (enthalpy) increases

  5. Energy and Phase Changes: Quantitative Treatment Melting: Heat of Fusion (DHfus) for Water: 333 J/g Boiling: Heat of Vaporization(DHvap) for Water: 2256 J/g

  6. Total Quantitative Analysis Convert 40.0 g of ice at –30 oC to steam at 125 oC Warm ice: (Specific heat = 2.06 J/g-oC) Melt ice: Warm water (s.h. = 4.18 J/g-oC)

  7. Total Quantitative Analysis Convert 40.0 g of ice at –30 oC to steam at 125 oC Boil water: Warm steam (s.h. = 1.92 J/g-oC)

  8. Enthalpy Change and Bond Energies DH = energy needed to break bonds – energy released forming bondsExample: formation of water: DH = [498 + (2 x 436)] – [4 x 436] kJ = -482 kJ

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