Molecular formula. Molar mass (g.mol-1). ΔcH0 (kJ.mol-1) Petrol C8H18 * 114 - 5470 Diesel C20H42 * 282 - 8090 Natural gas. CH4 16 - 890 Hydrogen. H2 2 - 286 Methanol. CH3OH 32 - 726 *Petrol and diesel are complex mixtures of hydrocarbons. On average, their properties resemble those of C8H18 and C20H42, respectively. 1.1) Calculate the energy density (in kJ.g-1) for all the fuels in the table above. Use the molar masses supplied in the table. 1.2) Why would you say that Space Shuttles rather use hydrogen as its primary fuel source instead of one of the other fuels in the table? 1.3) Formula 1 racing cars use petrol as their fuel source. In the USA, “Indy cars” use methanol as fuel source and in South Africa farmers use diesel as fuel source for their tractors. If all these motors perform equally optimally, which vehicle is the most fuel efficient? Give a reason for your answer.
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
|
Molecular formula. |
Molar mass (g.mol-1). |
ΔcH0 (kJ.mol-1) |
|
|
Petrol |
C8H18 * |
114 |
- 5470 |
|
Diesel |
C20H42 * |
282 |
- 8090 |
|
Natural gas. |
CH4 |
16 |
- 890 |
|
Hydrogen. |
H2 |
2 |
- 286 |
|
Methanol. |
CH3OH |
32 |
- 726 |
*Petrol and diesel are complex mixtures of hydrocarbons. On average, their properties resemble those of C8H18 and C20H42, respectively.
1.1) Calculate the energy density (in kJ.g-1) for all the fuels in the table above. Use the molar masses supplied in the table.
1.2) Why would you say that Space Shuttles rather use hydrogen as its primary fuel source instead of one of the other fuels in the table?
1.3) Formula 1 racing cars use petrol as their fuel source. In the USA, “Indy cars” use methanol as fuel source and in South Africa farmers use diesel as fuel source for their tractors. If all these motors perform equally optimally, which vehicle is the most fuel efficient? Give a reason for your answer.
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