Thermo_1 - THERMOCHEMISTRY or Thermodynamics Geothermal...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: THERMOCHEMISTRY or Thermodynamics Geothermal power —Wairakei —Wairakei North Island, New Zealand 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 This can be set up to provide ELECTRIC ENERGY in a fuel cell. in • Burning peanuts supply sufficient energy to boil a cup of water. • Burning sugar (sugar reacts with KClO3, a strong oxidizing agent) • These reactions are PRODUCT FAVORED • They proceed almost completely from reactants to products, perhaps with some outside assistance. Oxidation: Reduction: 4 OHe- 2 H2 ---> 4 H+ + 4 e---> + O2 + 2 H2O ---> 4 Page 1 Energy and Chemistry Energy and Chemistry ENERGY is the capacity is to do work or transfer heat. Potential & Kinetic Energy Potential & Kinetic Energy Potential energy — energy a motionless body has by virtue of its position. 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 HEAT is the form of is energy that flows between 2 objects because of their difference in temperature. Other forms of energy — • light • electrical NaCl — composed of Na+ and Cl- ions. and ions. 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 Kinetic energy — energy of motion • Translation Potential & Kinetic Energy Potential & Kinetic Energy Kinetic energy — energy of motion. rotate vibrate translate Page 2 INTERNAL ENERGY INTERNAL ENERGY (E) (E) • PE + KE = Internal energy (E or U) • Int. E of a chemical system Int. depends on • number of particles • type of particles • temperature INTERNAL ENERGY INTERNAL ENERGY (E) (E) • PE + KE = Internal energy (E or U) Internal Energy • The higher the T the higher the internal energy • So, use changes in T (∆T) to monitor changes in E (∆E). Thermodynamics Thermodynamics • Thermodynamics is the science of heat (energy) transfer. Energy and Chemistry Energy and Chemistry All of thermodynamics depends on the law of CONSERVATION OF ENERGY. ENERGY. • The total energy is unchanged in a chemical reaction. PE Energy Change in Energy Change in Chemical Chemical Processes Processes Reactants Kinetic Energy Products Heat energy is associated with molecular motions. • If PE of products is less than reactants, the difference must be released as KE. PE of system dropped. KE increased. Therefore, you often feel a T increase. Page 3 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 1 cal = 4.184 joules HEAT CAPACITY The heat required to raise an object’s T by 1 ˚C. Specific Heat Capacity Specific Heat Capacity 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 c) specific heat capacity specific Specific heat capacity = James Joule 1818-1889 Which has the larger heat capacity? heat lost or gained by substance (J) (mass, g)(T change, K) Specific Heat Capacity Specific Heat Capacity Substance Spec. Heat (J/g•K) H2 O 4.184 Ethylene glycol 2.42 Al 0.902 glass 0.84 Aluminum 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) 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)( ∆T) where ∆T = Tfinal - Tinitial q = (0.902 J/g•K)(25.0 g)(37 - 310)K q = - 6160 J Page 4 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 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) Heat Transfer and Heat Transfer and Changes of State Changes of State Liquid ---> Vapor Requires energy (heat). This is the reason a) you cool down after swimming b) you use water to put out a fire. q = - 6160 J Notice that the negative sign on q Notice signals heat “lost by” or transferred out of Al. + energy + energy Heating/Cooling Curve for Heating/Cooling Curve for Water Water See Figure 6.9 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. 2. 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? To melt ice To raise water from 0 oC to 100 oC 3 Heat water Evaporate water 4 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 q = (500. g)(333 J/g) = 1.67 x 10 5 J q = (500. g)(4.2 J/g•K)(100 - 0)K = 2.1 x 10 5 J 3. To evaporate water at 100 oC q = (500. g)(2260 J/g) = 1.13 x 10 6 J 4. Total heat energy = 1.51 x 106 J = Total 12 Melt ice +333 J/g +2260 J/g 1510 kJ Page 5 There’s more? Enthalpy! Page 6 ...
View Full Document

This note was uploaded on 01/11/2011 for the course ENGINEERIN MAE 107 taught by Professor Pozikrizdis during the Fall '08 term at San Diego.

Ask a homework question - tutors are online