Transcript Alkanes 1
Chapter 9 Energy and Hydrocarbons Chapter Outline Background & Energy from Fuels Alkanes: Backbone of Organic Chemistry Alkenes and Alkynes: Reactive cousins of Alkanes Cyclic Hydrocarbons Petroleum Natural Gas Coal Methanol (Gasohol) Define some terms Energy is a common idea that ran through the first half of the class. – – – – – – What is Energy? What is Heat? What is Temperature? What is the difference between heat and temperature? What are the ‘units’ of each measurement? Exothermic vs. Endothermic Energy Energy is defined as ‘the capacity to do work’ – What does this mean to you? Energy: Capacity to do work or to transfer heat! Types of Energy Kinetic Energy – Energy of Motion Ek = ½ mv2 m= mass (kg) v = velocity (m/s) Ek = Joules Potential Energy – Stored energy based on the position of one object with respect to another Ep = m *g* h m = mass (kg) g = gravitational constant = 9.806 m/s2 h= distance above reference Example What is the kinetic Energy of a bowling ball moving at a velocity of 1.5 m/s? (Mass of bowling ball = 7.5 kg) Ek = ½ mv2 Units of Energy Heat can have the following units – – – – – – – – Joules (J) = 1 kg*m2/s2 Kilojoules(kJ) calories (cal) = 4.184 Joule Kilocalories (kcal) = 1000 calories Dietary Calories = Calories (Cal) = 1 kcal Erg BTU Foot-pounds Energy Calculate the amount of potential energy of a 1 kg book raised about 6 ft (~2 meters) into the air. First Law of Thermodynamics Energy is neither created nor destroyed. – The Energy is said to be “transferred or transformed”! What happened to the energy of the book? Heat vs. Temperature Some of the energy was transformed to sound energy and some converted to heat! WHAT IS HEAT? – Before we consider heat … let’s look at temperature! Temperature Think back to global warming – vibrating molecules caused an increase in temperature Temperature – average kinetic energy of molecules in a substance. What is Heat? Heat is the total amount of energy in a substance – In other words – its the amount of thermal energy that a system contains. Heat Energy = (specific heat)*(amount of substance)*(Temperature) What’s the difference between Heat and Temperature? Think of this Example – A drop of boiling water and 4 liters of boiling water. Which one has more energy? What is a calorie? Based on the work of James Joule (late 1800’s) – One calorie = amount of heat required to raise 1 gram of water 1 degree Celsius. – One calorie = 4.184 Joules Units of Energy Heat can have the following units – – – – – – – – Joules (J) = 1 kg*m2/s2 Kilojoules(kJ) calories (cal) = 4.184 Joule Kilocalories (kcal) = 1000 calories Dietary Calories = Calories (Cal) = 1 kcal Erg BTU Foot-pounds Some ‘exercises’ 1. How many joules are in 425 Cal? 2. How much energy is required to raise 1 gram of water 1oC? 3. How much energy is required to raise 1000 grams (1 kg) of water from room temperature (25oC) to boiling (100oC) ? Exothermic vs. Endothermic Draw energy diagrams for the following processes. – Dissolving of Urea in water – Dissolving of Ethanol in water 9.1 Energy from Fuels Source of Energy used in the United States - 2000 Renewable 7% Natural Gas 24% Petroleum 38% Coal 23% Nuclear 8% Most of our energy comes from Fossil Fuels (Petroleum, Coal, Natural Gas) Combustion of Natural Gas Natural Gas is mostly Methane Consider the complete combustion of methane ____ CH4 + ____ O2 -> ____ CO2 + ____ H2O Methane Oxygen Carbon dioxide Is Energy Produced? How much? Water What determines if Energy is released or absorbed in a chemical reaction? Bond Energies!! BOND ENERGIES H C N O S F Cl Br I C=C C=C N=N N=N Single Bonds H C N 432 411 346 386 305 167 459 358 201 363 272 565 485 283 428 327 313 362 285 295 213 - 602 835 418 942 O S F 142 190 218 201 201 226 284 255 217 - 155 249 249 278 Multiple Bonds C=N 615 N=O 607 O=O 494 C=O 799 Cl Br I 240 216 190 208 175 149 C=O 1072 Bond Energies are given in kJ/mole