BS Chemistry 3
1. Assume that diesel fuel is C14H30 and that gasoline is octane. a. Calculate the amount of energy (heat) – in kcal - each releases per gram when combusted. b. Compare each as fuel for trucks.
c. Why do so many large trucks have diesel engines?
C8H18 (l) + 252O2 (g) 8CO2 (g) + 9H2O (g)
Standard Bond energies:
H-C| 99 kcal/mol|
C-C| 83 kcal/mol|
O=O| 119 kcal/mol|
C=O| 192 kcal/mol|
H-O| 111 kcal/mol|
Heat= [16(192)+18(111)] – [50(119)+18(99)+14(83)]
= 5,070 kcal/mol – 8,894 kcal/mol
= -3,824 kcal/mol
= -33.47 kcal/g C8H18
C14H30 (l) + 432O2 (g) 14CO2 (g) + 15H2O (g)
Heat= [28(192)+30(111)] – [43(119)+14(99)+26(83)]
= 8,706 kcal/mol – 8,661 kcal/mol
= 45 kcal/mol
= 0.3938 kcal/g C14H30
Diesel and gasoline are two main sources of energy for today’s cars. Both are from the same source, crude oil but are refined differently. These sources also have different chemical properties and each are burned in different ways. Diesel is easier to refine than gasoline, contains more energy than gasoline and the vehicle’s engine combustion process is more efficient. Diesel is denser and contain’s 11% more energy. It is more efficient in converting mechanical work because it operates at higher compression ratios and temperatures. Large trucks and agricultural vehicles have diesel engines to take advantage of this higher efficiency. Vehicles that use gasoline have to use spark plugs in order to ignite the fuel, which is due to the fact that gasoline engines have low compression ratio. The gasoline and air are combined and forced into the cylinder and compressed. The soark plug fires causing the mixture to ignite and explode, forcing the piston up and gives the car power. Diesel engines have much higher compressio ratios and does not anymore utilize spark...