Combustion Rapid chemical combination of a substance with oxygen, producing heat and light. Burning Exothermic chemical reaction. Creates heat (light glowing/flame) Fuels = organic compounds (especially hydrocarbons) in the gas, liquid or solid phase.

Candles are made out of Paraffin Wax. The chemical formula for Paraffin is C20H42. Melting point = 47 to 65 oC Boiling Point = <188oC Flash point = 198oC Flame Temperature = 1400oC

A molecule of Paraffin has the following structure. The combustion reaction for Paraffin is: 2 C20H42 + 61 O2 g 40 CO2 + 42 H2O This assumes that there is enough oxygen to completely react with the paraffin. The reaction that takes place follows the sequence of events shown on the following slides.

An oxygen molecule collides with the Paraffin molecule and reacts with that portion of the molecule.

This breaks the molecule into smaller segments and draws off a Carbon atom and two Hydrogen atoms to form Carbon monoxide and Water.

Another oxygen molecule collides with the Paraffin molecule and reacts with that portion of the molecule.

This breaks the molecule into even smaller segments and draws off another Carbon atom and two more Hydrogen atoms to form Carbon monoxide and Water. An oxygen molecule collides with the 2 Carbon monoxide atoms that were formed in the previous 2 steps to form 2 Carbon dioxide molecules.

As long as there is enough oxygen available this reaction will take place as described in the balanced equation. However, If the amount of oxygen is limited then some of the small segments and Carbon monoxide molecules that were produced will not get used up. This is referred to as “Incomplete Combustion”.

The unbalanced equation for the incomplete combustion of Paraffin is: We do not normally balance incomplete reactions since there is too much variation in the possible products. The unbalanced equation for the incomplete combustion of Paraffin is: C20H42 + O2 g CO2 + CO + H2O + assorted particulates The “assorted particulates” are the short segments that were produced.

Properties of Carbon Monoxide: Gas Colorless Odorless Tasteless Inhibits oxygen intake Undetectable by humans Can be poisonous or fatal to humans and animals

Health Impact of Carbon Monoxide Poisoning: Fatigue Headache Dizziness Nausea Vomiting Disorientation Loss of consciousness Environmental Impact of Carbon Monoxide: Contributes to global warming Component of smog