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

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)

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

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

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)

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

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

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)