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Thermodynamics

Energy and energy transformations. Thermodynamics. First Law of Thermodynamics. Energy is never created nor destroyed Energy can change forms, but the quantity is always constant. Second Law of Thermodynamics. The Entropy of the Universe is always increasing Entropy= disorder.

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Thermodynamics

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  1. Energy and energy transformations Thermodynamics

  2. First Law of Thermodynamics • Energy is never created nor destroyed • Energy can change forms, but the quantity is always constant.

  3. Second Law of Thermodynamics • The Entropy of the Universe is always increasing • Entropy= disorder

  4. Third Law of Thermodynamics • The entropy of an ideal solid at zero Kelvin is zero • All molecular motion stops at 0 K

  5. Endothermic Reactions • Energy is used to begin a reaction • Products have higher energy than reactants • Absorbs heat from surroundings • Ice melting • Water evaporating

  6. Exothermic Reactions • Gives off energy during a reaction • Reactants have more energy than products • Gives off heat • Ice freezing • Water condensing

  7. Heat vs Temperature • Temperature- measure of average KE • Heat - measure of energy transfer • Temp change (∆T) depends on: • amount of heat transferred (q) • mass of object (m) • specific heat of the object (C) • Video link: http://www.youtube.com/watch?v=wTi3Hn09OBs&safety_mode=true&persist_safety_mode=1

  8. Measuring Heat • q = m C ∆T • q = heat • measured in joules (J) or kilojoules (kJ) • 1000J = 1kJ • m = mass; measured in grams (g) • ∆ T = change in temp • measured in Celsius (°C) or Kelvin (K) • C = specific heat • units are J/g°Cor J/gK

  9. Endo/exothermic • -q = release heat (exothermic) • +q= absorb heat (endothermic)

  10. What amount of heat is needed to increase the temp of 10 g of Hg by 5C? (specific heat of Hg is 0.139 J/gC) • If 68,000J of heat are added to 25g of H2O (specific heat of water is 4.184 J/gC), what is the change in temperature in Celsius?

  11. Calorimetry • Calorimetry • uses a closed system (calorimeter) to determine the energy change or specific heat of an unknown substance • Calorimeter- an insulated device usually filled with water or a substance with a known specific heat

  12. 1st law - conservation of energy • When applied to a closed system, any energy that is lost by one substance is gained by the other • qsubstance1= - qsubstance2 • since q = m C ∆ T… m1 C1∆ T1= - m2 C2 ∆T2

  13. Ex: A 55.8g piece of unknown metal at 180°C is placed into 100.0g of water that began at 25°C. The final temperature of both was 26.8°C. If the specific heat of water is 4.184 J/g°C, calculate the specific heat of the metal.

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