2. Combustion
Chemical reaction in which a fuel burns in oxygen to produce predictable products and a flame

3. Hydrocarbon Combustion
Hydrocarbons are molecular (covalent) compounds of the elements carbon & hydrogen
Many are used as fuels; ie methane, propane, gasoline and coal
Combustion reactions produce heat (thermal energy) & light (electromagnetic energy)

4. Complete or Incomplete?
All hydrocarbons burn, provided they are hot enough and have sufficient oxygen
Depending on the products that form, we classify combustion as either complete or incomplete

5. Complete Combustion Complete Combustion occurs when O2 is plentiful
It releases the most energy and the cleanest flames
General Equation:
CXHY + O2(g)  CO2(g) + H2O(g) + energy

6. Incomplete Combustion
Incomplete Combustion occurs when O2 is in limited supply
It releases less energy and results in inconsistent, sooty, yellow, cooler flames
Products (in addition to CO2 and H2O)
CO(g) (carbon monoxide)
C(s) (soot, ash, mixture of solid carbon products)

7. Problems of Incomplete Combustion
Inefficient- releases only a portion of the energy contained in the fuel
city/highway/idle
Soot- many chemicals in soot are toxic when inhaled, also builds up around engine
CO(g)- mistaken for O2 by hemoglobin in blood

8. Combustion Concerns
CO2 and H2O are greenhouse gases; contributing to global warming
Many fuels contain impurities such as sulfur and heavy metals that contribute to air pollution
Firefighters
Forest Fires

9. Catalytic Converter
This diagram shows how the polluting effects of nitrogen combustion in vehicle engines can be largely eliminated by catalytic conversion. Match each chemical equation to the correct position in the diagram.
Combustion in the engine
N2(g) + O2(g) → 2NO(g)
Without catalytic conversion
Catalytic conversion
2NO(g) → N2(g) + O2(g)
Further reaction in the atmosphere
2NO(g) + O2(g) → 2NO2(g)
Formation of acids in the atmosphere
2NO2(g) + H2O(l) → HNO3(aq) + HNO2(aq)