Thermo_1 - THERMOCHEMISTRY Geothermal power —Wairakei North Island New Zealand or Thermodynamics from the Saunders Interactive General Chemistry

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Unformatted text preview: THERMOCHEMISTRY Geothermal power —Wairakei North Island, New Zealand or Thermodynamics from the Saunders Interactive General Chemistry CD-ROM Energy & Chemistry Energy & Chemistry Energy and Chemistry 2 H2(g) + O2(g) --> 2 H2O(g) + heat and light • Burning peanuts peanuts supply sufficient energy to boil a cup of water. • Burning sugar (sugar reacts with KClO3, a strong oxidizing agent) • These reactions are PRODUCT These PRODUCT FAVORED • They proceed almost completely from reactants to products, perhaps with some outside assistance. Page 1 This can be set up to provide ELECTRIC ENERGY in a fuel cell. Oxidation: Reduction: 4 OH- 2 H2 ---> 4 H+ + 4 ee- + O2 + 2 H2O ---> 4 Energy and Chemistry Energy and Chemistry ENERGY is the capacity to do work or transfer heat. HEAT is the form of energy that flows between 2 objects because of their difference in temperature. Other forms of energy — • light • electrical Potential Energy on the Atomic Scale • Positive and negative particles (ions) attract one another. • Two atoms can bond • As the particles attract they have a lower potential energy Potential & Kinetic Energy Potential & Kinetic Energy Potential energy — energy energy a motionless body has by virtue of its position. Potential & Kinetic Energy Potential & Kinetic Energy Kinetic energy — energy of motion • Translation Page 2 Potential Energy on the Atomic Scale • Positive and negative particles (ions) attract one another. • Two atoms can bond • As the particles attract they have a lower potential energy NaCl — composed of Na+ and Cl- ions. Potential & Kinetic Energy Potential & Kinetic Energy Kinetic energy — energy of motion. rotate vibrate translate INTERNAL ENERGY INTERNAL ENERGY (E) (E) INTERNAL ENERGY INTERNAL ENERGY (E) (E) • PE + KE = Internal energy (E or U) • Int. E of a chemical system depends on • number of particles • type of particles • temperature • PE + KE = Internal energy (E or U) Thermodynamics Thermodynamics • Thermodynamics is the science of heat (energy) transfer. • The higher the T the higher the internal energy • So, use changes in T (ΔT) to monitor changes in E (ΔE). Energy and Chemistry Energy and Chemistry All of thermodynamics depends on the law of CONSERVATION OF ENERGY. • The total energy is unchanged in a chemical reaction. Heat energy is associated with molecular motions. Internal Energy • If PE of products is less than reactants, the difference must be released as KE. Page 3 PE Energy Change in Energy Change in Chemical Chemical Processes Processes Reactants Kinetic Energy Products PE of system dropped. KE increased. Therefore, you often feel a T increase. UNITS OF ENERGY UNITS OF ENERGY 1 calorie = heat required to raise temp. of 1.00 g of H2O by 1.0 oC. 1000 cal = 1 kilocalorie = 1 kcal 1 kcal = 1 Calorie (a food “calorie”) But we use the unit called the JOULE called JOULE 1 cal = 4.184 joules HEAT CAPACITY The heat required to raise an object’s T by 1 ˚C. James Joule 1818-1889 Substance Spec. Heat (J/g•K) H2 O 4.184 Ethylene glycol 2.42 Al 0.902 glass 0.84 Aluminum How much energy is transferred due to T difference? The heat “lost” or “gained” is related to a) sample mass b) change in T and b) change c) specific capacity = c) Specific heat heat capacity specific Which has the larger heat capacity? Specific Heat Capacity Specific Heat Capacity Specific Heat Capacity Specific Heat Capacity Specific Heat Capacity Specific Heat Capacity If 25.0 g of Al cool from 310 oC to 37 oC, how many joules of heat energy are lost by the Al? Specific heat capacity = heat lost or gained by substance (J) (mass, g)(T change, K) Page 4 heat lost or gained by substance (J) (mass, g)(T change, K) Specific Heat Capacity Specific Heat Capacity If 25.0 g of Al cool from 310 oC to 37 oC, how many joules of heat energy are lost by the Al? heat gain/lose = q = (sp. ht.)(mass)( ΔT) where ΔT = Tfinal - Tinitial q = (0.902 J/g•K)(25.0 g)(37 - 310)K q = - 6160 J Specific Heat Capacity Specific Heat Capacity If 25.0 g of Al cool from 310 oC to 37 oC, how many joules of heat energy are lost by the Al? q = - 6160 J Notice that the negative sign on q Notice signals heat “lost by” or transferred out of Al. Heating/Cooling Curve for Heating/Cooling Curve for Water Water Heat water Evaporate water 4 Heat Transfer and Heat Transfer and Changes of State Changes of State Changes of state involve energy Ice -----> Water Requires 333 J/g (heat of fusion) Liquid ---> Vapor Requires energy (heat). This is the reason a) you cool down after swimming b) you use water to put out a fire. + energy Heat and Changes of State Heat and Changes of State What quantity of heat is required to melt 500. g of ice and heat the water to steam at 100 oC? See Figure 6.9 3 Heat Transfer and Heat Transfer and Changes of State Changes of State Heat of fusion of ice = 333 J/g Heat of fusion of ice = 333 J/g Specific heat of water = 4.2 J/g•K Specific heat of water = 4.2 J/g•K Heat of vaporization = 2260 J/g Heat of vaporization = 2260 J/g 12 Heat and Changes of State Heat and Changes of State What quantity of heat is required to melt 500. g of ice and heat the water to steam at 100 oC? 1. 1. +333 J/g +2260 J/g To melt ice To q = (500. g)(333 J/g) = 1.67 x 10 5 J (500. 2. To raise water from 0 oC to 100 oC q = (500. g)(4.2 J/g•K)(100 - 0)K = 2.1 x 10 5 (500. J 3. Melt ice + energy To evaporate water at 100 oC q = (500. g)(2260 J/g) = 1.13 x 10 6 J (500. 4. Total heat energy = 1.51 x 106 J = 4. Total 1510 kJ Page 5 There’s more? Enthalpy! Page 6 ...
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This note was uploaded on 10/19/2011 for the course CHM 2210 taught by Professor Reynolds during the Fall '01 term at University of Florida.

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