Petroleum B

1. Petroleum B Petroleum as an energy source

2. Buried Sunshine • Fossil fuels - oil, coal, natural gas, are all dead plants which grew be photosynthesizing sunlight. • Therefore, fossil fuels are buried sunlight. • There is no 100% conclusive evidence of where petroleum comes from. • The process of making fossil fuels over time happens too slow.

3. Potential vs. Kinetic Energy • Potential Energy is stored energy. • Chemical energy is a kind of potential energy = battery • Kinetic Energy is energy of movement/motion • During a chemical reaction the potential energy in compounds are released and the products (usually) have less potential energy than the reactants.

4. Bond breaking and bond making • In a chemical reaction, bonds must first be broken. • Combustion of methane • CH4 + O2 CO2 + H2O • The methane and oxygen molecules must first be broken. This requires energy to be ADDED = Endothermic • Next, the bonds must reform, but in different combinations. When this happens it is an exothermic reaction = energy is released

5. Potential Energy Diagram-Exothermic Reaction

6. Potential Energy Diagram-Endothermic Reaction

7. Bond breaking and bond making • If the energy added (endothermic) is greater than the energy given off (exothermic), then the overall reaction is ENDOTHERMIC. • If the energy added (endothermic) is less than the energy given off (exothermic), then the overall reaction is EXOTHERMIC.

8. Bond breaking and bond making • EXOTHERMIC = feels hot to the touch • energy was released to the environment • ENDOTHERMIC = feels cold to the touch • Energy was absorbed from the environment

9. Energy Conversion • Consider the energy required to power a hair dryer. • No matter how many times energy is transformed to another energy it is never “used up”. • Law of Conservation of Energy - energy is never created or destroyed, it only changes forms.

10. Energy Efficiency • Devices that convert chemical energy (fossil fuels) to thermal energy (heat) then to mechanical energy (movement) are less than 50% efficient - this refers to the energy made by power plants. • Solar cells and fuel cells (for cars) are cleaner and more efficient. • Some energy is always “lost” when it is converted from one form to another.

11. Energy Efficiency • Low efficiency of the machine using the energy. • The most efficient car engines are only 25% efficient. The rest of the energy is lost as heat. • Do B.5 Energy Conversion Efficiency Problems on p 245.

12. Combustion • BURNING!! • Burning a hydrocarbon will always yield Carbon Dioxide (CO2) and Water (H2O) • Energy is always released - it feels hot. C25H52 + O2 CO2 + H2O combustion of candle wax. • Where does the energy come from? • The chemical bonds release energy when they are destroyed.

13. Specific Heat Capacity Specific Heat Capacity - the amount of heat needed to raise the temperature of a substance by 1C.

14. Calculating Specific Heat Capacity • Suppose a 10.0 g water sample is heated from 25.0C to 30.0C. How much energy must have been added to the water? • 210 J of heat

15. Heat of Combustion/Molar Heat of Combustion • Heat of Combustion - the amount of heat given off when an amount of a substance is burned • The “amount” is usually 1 gram. • Measured in kJ/g • Molar heat of combustion - the amount of heat given off when 1 mole of any substance in burned. • Measured in kJ/mol

16. Calculating Heat of Combustion • How much energy (in kilojoules) is released when 76.0 g of hectane is burned?

17. Calculating Molar heat of combustion • How much energy (in kJ) is released by completely burning 25.0 mol hexane. • 104000 kJ

18. Altering Fuels • There are only 9.9 gallons of gasoline in a 55 gallon drum of crude oil after fractional distillation. • Now, as much as 25.9 gallons (47%) of gasoline can be taken from a 55 gal. drum of crude oil because of altering of molecules • Scientists can change existing molecules to meet the demand.

19. Cracking • Cracking - process of converting large hydrocarbon molecules to smaller ones through the application of heat (600C-700C) and catalysts. • Kerosene: 16 C’s to gasoline 8 C’s • Hydrocarbons up to about 14 C’s can be produced through cracking.

20. Cracking • Catalysts are used to speed up existing reactions but they themselves are not used up. • Catalytic cracking is more efficient because it requires less heat • Bonus: During cracking Methane, ethane, propane, and butane made and immediately burned to keep the temp. hot.

21. Pinging/Knocking • “Gasoline” is composed mainly of straight chained molecules of: hexane, heptane, and octane. • Gas-Air mixture is first compressed in the cylinder (piston) just before it is ignited by the spark plug. • Sometimes the compressed gas explodes before the spark plug ignites it. • This causes the piston to bang back against the crankshaft = pinging/knocking • These burn to rapidly - to hot causing the engine to “ping” or “knock.” • Branched-chain alkanes burn more favorably in car engines

22. This is the best “octane” - isooctane

23. Octane Rating • “Gasoline” is sold at varying grades. • Isooctane is assigned an octane number of 100. • Straight-chained Heptane is assigned an octane number of 0. • Heptane has very poor engine performance.

24. Finding Octane Rating • Octane rating is determined under two conditions: • A free-running engine • And engine pulling a load (towing) • The results of these two processes are averaged together. • The higher the rating the more anti-knock • Refer to the following for more information: http://auto.howstuffworks.com/question90.htm

25. Octane rating • Leaded Fuel: tetraethyl lead was added to gasoline to increase octane rating. • However, it added lead compounds to environment.

26. Oxygenated Fuels • With lead-based fuel out, an alternative had to be found. • Oxygenated fuels - a blend of additives added to fuel to increase the octane rating. • The molecules of the additives contain oxygen as well as C and H.

27. Oxygenated Fuels • Oxygenated fuel provide LESS energy per gallon = less miles per gallon. • BUT, they increase octane number (better performance of car) while reducing exhaust pollutants, and less emissions like CO.

28. Oxygenated Fuels • Methanol is a common oxygenated fuel (CH3OH). • An additive to fuel • Boosts octane rating (better engine performance). • Methanol can be made from coal, natural gas, wood, and corn • Conserves nonrenewable resources • Gasohol - blend of 10% ethanol, 90% gasoline • Can be used without engine modifications

29. Oxygenated Fuels • MTBE (methyl tertiary-butyl ether) was added to gas in late 1970’s. • Octane rating of 116 - pollution reducing oxygenating chemical. • However,late 1990’s: bad gas storage units allowed MTBE to seep into groundwater. Unpleasant taste to water; became a concern even though no apparent health risk. • MTBE since them has been phased out.

30. Oxygenating fuels • MTHE (methyltetrahydrofuran) • Octane rating = 87 same as gasoline • It can increase the level of oxygenated fuel • Can be obtained from renewable resources like papermill waste products.

31. Straight-chain to branched-chain • Straight-chained hydrocarbons burn too hot. • Branched-chained hydrocarbons burn more favorably. • Scientists can convert straight-chained to branched-chained. • The straight-chained vapor is heated with a catalyst • This is called isomerization.