Lecture Notes: Energy, Fuels, and Combustion
Introduction
- Focus on energy, specifically fuels and combustion.
- Understanding complete combustion of carbon and hydrogen-based fuels.
- Writing thermochemical equations for combustion.
Thermochemical Equations
- Definition: Outline energy released/absorbed during chemical processes.
- Components:
- Mole ratio of reactants and products.
- Physical states (solid, liquid, gas, solution).
- Heat energy (ΔH - Enthalpy change).
Complete Combustion
- Involves fuel reacting with oxygen to produce CO2 and H2O.
- Example:
- Octane:
- Liquid at room temperature.
- Balanced equation: C8H18 + 25/2 O2 → 8 CO2 + 9 H2O, ΔH = -5417 kJ/mol.
- Ethanol:
- Balanced equation: C2H5OH + 3 O2 → 2 CO2 + 3 H2O, ΔH = -1371 kJ/mol.
Incomplete Combustion
- Produces carbon (soot) and carbon monoxide.
- More likely with longer-chain carbon fuels.
- Causes:
- Oxygen deficiency.
- Redox process affecting oxidation states.
- Example: Methane undergoing incomplete combustion.
- Lower oxidation states: Carbon monoxide (+2), Carbon (0).
Bunsen Burner Example
- Closed air hole: Yellow flame (incomplete combustion).
- Open air hole: Blue flame (complete combustion, more heat).
Factors Affecting Combustion
- Chain Length: Larger fuels require more oxygen.
- Dispersion Forces: Reduce mixing of fuel and oxidant.
Experiment: Alkane vs. Alkene
- Compare combustion of hexane and hexene.
- Hexene produces more soot (darker filter paper).
Issues of Incomplete Combustion
- Carbon Monoxide:
- Strong binder to hemoglobin.
- Limits oxygen transport, leads to health issues.
- Carbon (Soot):
- Visual pollutant.
- Reduces photosynthesis, can aggravate respiratory issues.
- Acts as a greenhouse gas, trapping heat.
Conclusion
- Summary of undesirable consequences of incomplete combustion.
- Highlights issues related to health and environmental effects.
This concludes the lecture on fuels and combustion. Look forward to the next part in the series for further insights.