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Published byCordelia Lawrence Modified over 9 years ago
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Energy and energy transformations
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First Law of Thermodynamics Energy is never created nor destroyed Energy can change forms, but the quantity is always constant.
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Second Law of Thermodynamics The Entropy of the Universe is always increasing Entropy= disorder
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Third Law of Thermodynamics The entropy of an ideal solid at zero Kelvin is zero All molecular motion stops at 0 K
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Endothermic Reactions Energy is used to begin a reaction Products have higher energy than reactants Absorbs heat from surroundings Ice melting Water evaporating
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Exothermic Reactions Gives off energy during a reaction Reactants have more energy than products Gives off heat Ice freezing Water condensing
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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=wTi 3Hn09OBs&safety_mode=true&persist _safety_mode=1 http://www.youtube.com/watch?v=wTi 3Hn09OBs&safety_mode=true&persist _safety_mode=1
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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°C or J/gK
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Endo/exothermic -q = release heat (exothermic) +q= absorb heat (endothermic)
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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 H 2 O (specific heat of water is 4.184 J/g C), what is the change in temperature in Celsius?
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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
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1st law - conservation of energy When applied to a closed system, any energy that is lost by one substance is gained by the other q substance1 = - q substance2 since q = m C ∆ T… m 1 C 1 ∆ T 1 = - m 2 C 2 ∆T 2
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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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