VIEWS: 16 PAGES: 4 POSTED ON: 5/11/2011 Public Domain
C + O2 CO2 + Energy 6 million light bulbs Thus, note that for every atom of carbon, we produce one $13 million of molecule of CO2. fluorescent bulbs This will turn out to be one of the major factors in the Saving 60 increase in carbon dioxide in the atmosphere (a greenhouse MWatts gas). Does this sound like a good idea? A) Yes B) No Clicker Question Each reaction with a carbon atom (in the coal for example), has With this energy (107 Joules), approximately how many feet an energy of 10-18 Joules. can we raise a 3000 lb car? Assume 100% efficient use of this energy. This seems like a tiny number! But it is only one carbon atom. Unit Conversions: A) 4 feet B) 10 feet 1 Joule = 0.74 foot-pounds How many atoms are there in 12 grams of carbon? 1 Joule = 0.0009 Btu C) 200 feet D) 2300 feet 1 Joule = 0.24 calories Avagadro’s Number = 6 x 1023 atoms per mole per 12 grams of carbon Solution: ⎛ 0.74 ftlbs ⎞ A 1 pound lump of coal has about 1025 atoms of carbon. Thus Energy = (10 7 J ) × ⎜ ⎟ the total energy from this chemical reaction is: ⎝ J ⎠ Energy = 7 ×10 6 ft − lbs Total Energy = (Energy per Carbon Atom )× (# Carbon Atoms) ( ) Total Energy = 10 -18 Joules/Atom × (10 25 Atoms) = 10 7 Joules Thus, the work that can be done is lifting a 3000 lbs car x 2300 feet ~ 7 x 106 ft-lbs. Energy Unit Calorie and calorie! Where is the energy given on this label? calorie New Energy Unit = Food Calorie or Calorie Energy to change the 1 Food Calorie = 4184 Joules temperature of 1 gram of water by 1 °C Calorie or Food Calorie (or kilo- calorie) Energy to change the temperature kilo- 1° of 1 kilo-gram of water by 1°C * Thus a Food Calorie is actually the same as 1000 calories (which is the physics or chemistry term). 1 British Thermal Unit (BTU) Energy required to change the 1° temperature of 1 pound of water by 1°F So really that is 1000 physics calories! Clicker Question Table 2.6 says that the best coal (Anthracite) which is 88% carbon, has an energy content of 13,300 Btu / lb. So how many degrees can you raise the temperature of 260 pounds of water with the energy from one pound of coal? 1 Jelly donut CO2 + H2O + Energy A) 5 degrees Fahrenheit (250 Calories) B) 50 degrees Fahrenheit C) 250 degrees Fahrenheit How many Joules of energy is this? D) 3000 degrees Fahrenheit E) 40 degrees Celsius ⎛ 1000 calories ⎞ ⎛ 4.184 Joules ⎞ 250 Calories × ⎜ ⎟×⎜ ⎟ = 106 Joules ! 13,300 Btu raises the temperature of 1 lbs of water by 13,300 0F ⎝ 1 Calorie ⎠ ⎝ 1 calorie ⎠ OR 13,300 Btu raises the temperature of 260 lbs of water by 13,300/260 = 50 0F What if we compare this 1 million Joules from the donut, to the Other forms of Energy? Potential Energy of a 60 kg object at a given height (H). What is that height H? PE = mgH PE (10 6 Joules) H= = mg (60kg × 9.8m / s 2 ) PE (106 Joules) Demonstration with hammering a nail into a board. H= = mg (60kg × 9.8m / s 2 ) 1. Work is done by the person to give Kinetic Energy to the hammer. H = 1700 meters or 5000 feet 2. The hammer then does work on the nail to give it kinetic energy (the nail moves with some velocity). Biological mechanism needed for efficient conversion. 3. When the nail stops moving, where did the energy go? 2 New From of Energy = Heat ! Thus, when we convert energy into heat or thermal energy, Heat was not considered a form of energy until the mid- the kinetic energy is not seen as the net motion of a large 1800’s. Prior to that it was thought of as some type of object (like a car or a nail), but instead as an increase in the fluid that made things hot. velocity of individual particles with random motion. In fact heat energy (also called thermal energy) is really Since the motion is random, the object does not appear to just a microscopic form of kinetic energy. move, but just has a higher temperature. Temperature is typically proportional to the average Kinetic Energy of particles in a material. Note that thermal energy can be hard to use (get at) or convert into other forms. Another Energy Mass Energy Here is me lecturing…. Over 100 years ago, Albert Einstein How much energy do I have? discovered that mass is just another form of energy. Weight = 185 pounds E = mc 2 Convert weight in earth’s gravity to mass 84 kg E = mc 2 = (84kg )× (3 ×108 m / s ) 2 E = 8 ×1018 Joules ! m is mass in kilograms (SI Units) and c is the speed of light (3 x 108 meters/second). Consider that the entire USA uses 100 QBtu or 1020 Joules each year. Thus the energy in my body could “run all the lights” for 29 out of 365 days in a year. What is the problem with this idea? Clicker Question However, in nuclear reactions, we sometimes observe that Fission Energy Release there was a little more mass before compared with afterwards. U235 + n Ba141 + Kr92 + 3n U235 + n Te139 + Zr94 + 3n Fission Reaction (Splitting) Fusion Reaction (Adding) If you add the masses before and after, you find that you lost about 3 x 10-28 kilograms in the process! Recalling that E=mc2 (where c = 3 x 108 m/s), what is the ratio of energy from 235 grams of Uranium (1023 atoms) compared to that from a 1 pound lump of coal (107 Joules)? A) Uranium and coal energies are about equal B) Uranium energy is 1/100 of the coal energy C) Uranium energy is 1000 times the coal energy D) Uranium energy is 100,000 times the coal energy E (Uranium) = mc 2 = (10 23 × (3 × 10 −28 kg ))(3 ×108 m / s) 2 ~ 1012 J 3 Nuclear fission chain reactions are the current power source for nuclear reactors. Isotopes of Uranium for example are the fuel. Nuclear weapons now utilize both fission and fusion reactions. Chemical Reactions Nuclear Reactions involve involve atomic electrons. proton and neutrons in the nucleus. Typical energy per reaction ~ 10-18 Joules Typical energy per The sun is powered by fusion (or 10 eV) reaction ~ 10-11 Joules reactions in the core. The sun will (or 200 MeV) continue to “burn” for a few billion more years before it runs out of fuel. 4