What are the by-products of alkene combustion?

The by-products of alkene combustion are carbon dioxide (CO2) and water (H2O).

When alkenes, which are hydrocarbons with a carbon-carbon double bond, undergo combustion, they react with oxygen in the air to produce carbon dioxide and water. This is a type of exothermic reaction, meaning it releases energy in the form of heat and light, which is why combustion reactions are commonly associated with fire or burning.

The general equation for the complete combustion of an alkene is CnH2n + (3n+1)/2 O2 → n CO2 + n H2O. This equation shows that for every molecule of alkene, you need (3n+1)/2 molecules of oxygen to produce n molecules of carbon dioxide and n molecules of water. For example, the combustion of ethene (C2H4), a common alkene, would be C2H4 + 3 O2 → 2 CO2 + 2 H2O.

However, it's important to note that this equation represents complete combustion, where there is enough oxygen present to fully react with the alkene. In cases of incomplete combustion, where there isn't enough oxygen, the reaction can also produce carbon monoxide (CO) and even solid carbon (C), both of which are harmful pollutants.

In summary, the combustion of alkenes primarily produces carbon dioxide and water, but can also produce carbon monoxide and solid carbon if the combustion is incomplete. This is why ensuring complete combustion in industrial processes and engines is important, to minimise the production of harmful by-products.