Combustion of Hydrocarbons
When hydrocarbons (compounds made of carbon and hydrogen) burn in oxygen, they undergo combustion reactions that always produce the same two products: carbon dioxide and water. It's like a chemical recipe that never changes!
Complete combustion happens when there's plenty of oxygen available. Take propane as an example: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O. Notice how the propane molecule gets completely broken down, with all the carbon becoming CO₂ and all the hydrogen becoming H₂O.
You can actually test for these products in the lab. Water vapour will turn anhydrous copper sulfate from white to blue, or change cobalt chloride paper from blue to pink. Carbon dioxide turns clear limewater milky white - a dead giveaway that combustion has occurred.
Incomplete combustion is the troublemaker that happens when oxygen runs low. Instead of harmless CO₂, you get dangerous carbon monoxide (CO). Using our propane example: C₃H₈ + 3½O₂ → 3CO + 4H₂O. This is why proper ventilation matters with gas appliances!
Quick Tip: Remember the difference - complete combustion needs MORE oxygen and produces CO₂, whilst incomplete needs LESS oxygen and produces deadly CO.