What is the exact characteristic that makes something flammable.

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Try to really boil it down please.

In: Chemistry

Something is combustible when it can react with air and heat to create a fire. Something is flammable when it can react with air and heat **at typical temperatures** and **easily** create a fire. For instance, a log is combustible, but not flammable, as it takes quite a bit for the log to catch fire at normal temperatures. Paper is combustible and flammable because it can catch fire easily at normal temperatures. Gasoline is also flammable, as liquid gasoline rapidly evaporates at normal temperatures and catches fire very easily.

Flammability is tied to combustibility.

Combustible materials are those that “easily catch fire” in a specific process we call “combustion”. Such process in chemistry is a fast highly-exothermic redox reaction.

“Fast” in a sense that the molecules react very rapidly in a short period of time. “Highly-exothermic” means that it releases a lot of energy in the form of heat. Combining the two, you get an event we call “fire”, i.e. rapid release of energy in the form of heat.

“Redox” reactions are specific chemical reactions involving transfer of electrons. In basic chemistry, common chemical reactions involve combining and breaking molecules composed of different atoms of elements. “Redox” takes this up a notch wherein electrons are also transferred. This process involves a lot of energy.

In “redox”, we have two types of reactants: electron-giver and electron-receiver. The best electron-receiver is oxygen molecule (O2) as it is a strong electron-receiver and is abundant in the open atmosphere. You should see by now, that the electron-giver is the reactant being “combusted” or “burned”. The better is as material as an electron-giver, the higher its combustibility.

Going back to flammability, it is the measure of how easily a **combustible** material ignites. A material may be combustible, but to start the reaction you will need an **ignition** – a sudden jolt of energy required to kickstart the redox reaction. Some materials cannot be “ignited” easily despite being combustible, due to various reasons.

Consider diesel which is a fossil fuel which definitely burns, i.e. a combustible material. It is usually labeled as nonflammable because you would need a large amount of energy for its ignition. This is why diesel-powered engines require spark plugs to start the combustion process. The electric spark is a high-energy ignitor.