Eli5: What makes the flammable gasses to be flammable?


Eli5: What makes the flammable gasses to be flammable?

In: Chemistry

Let’s use a simple one for an example-Hydrogen.

Hydrogen has one proton and one electron, the simplest atom. That one electron is in an energy level that is more stable with 2 electrons. That means that, with enough energy being put in it will form a bond with another atom that has room for it. Oxygen is one such atom, it has space for 2 electrons in its outer shell (8 is stable for all orbitals except the lowest). The hydrogens snap to the oxygen, releasing energy as they react to form water.

The same is true for all flammable materials, just more complex. They are more stable after reacting with oxygen, and with enough activation energy they will do so, releasing enough energy to cause a chain reaction.

Here’s a metaphor for you.

Imagine atoms are like a stage play. The protons and neutrons are up on stage and the electrons sit in the rows of seats as the audience.

*ALL* chemistry comes down to two conflicting desires –

1) Atoms HATE having incomplete audience members in the rows, they’d want either a full row or an empty row, they hate incomplete rows.

2) Atoms also HATE having more, or fewer, audience members than people on the stage.

So the happiest atoms have both, fully complete rows of audience members AND the same number of people in the crowd as onstage. These atoms are called “Nobel Gases” because they basically don’t interact with chemistry at all.

The unhappiest atoms have a row with just one audience member, or have just one empty seats. These are atoms like Hydrogen, Sodium, Chlorine, and Iodine. These atoms will have really POWERFUL chemistry because they are jussst sooooo close to being happy, they’ll do anything to lose the one electron, or gain one more. That’s why sodium and hydrogen are so explosive and why chlorine and iodine are used to kill microorganisms, they have really powerful chemistry.

Now some where in the middle you have atoms that have a half-full row. They would need to gain a bunch, or lose a bunch of electrons to have their rows filled, but that would mean they have really uneven audiance-to-performers balances, they hate that. So these atoms like to *do double shows* with other atoms, they essentially all get up on stage together and share their audiences. Everybody is happy. These are atoms like Oxygen, Carbon, Silicon, and Iron. What you’ll notice about these atoms is they form molecules really readily, and while the reactions might not be super powerful, they are really really happy and stable.

Technically iron “burns” the same way wood does, it chemically bonds with oxygen to form rust and gives off heat as a result. It just happens really slowly.

So to your point – why are some things flammable? These tend to be compounds that are agreeing to share the stage with other actors, and Oxygen is the fan-favorite here. Everyone loves oxygen. So hydrogen will burn with oxygen and form very stable water. Fossil fuels will burn with oxygen and form water and CO2 (note in fossil fuels example oxygen is sharing the stage with hydrogen to make water AND with carbon to form CO2). Wood burns the same way, oxygen comes in and shares the stage.