Fire can bring entire buildings to the ground in hours and can devastate entire forests
that have stood for thousands of years.
It's one of the most powerful forces of nature.
But what exactly is fire?
When we stare into a flame, what are we actually looking at?
Let's find out.
The ancient Greeks believed that the universe was made up of four basic elements, fire,
water, earth and air.
Their belief was built on the premise that you can touch and feel all of these things,
they believed they were the building blocks of all matter.
We now know that this isn't the case.
But the ancient Greeks got one thing in particular, very, very wrong.
They completely miss-classified fire, because, fire isn't an element at all.
Also it's not really matter either, well not completely anyway.
Fire is a mixture of gases such as oxygen, carbon dioxide, carbon monoxide and water
vapour, to name a few; mix those gases with photons of light and thermal energy and you
pretty much have the building blocks of fire.
Fire is actually the visible side effect of what happens when matter undergoes a change
of state by means of a chemical reaction.
Of course, you can't blame the Greeks, they did pretty well considering their level of
technological advancement.
But let's see if we can do a litter better with everything we now know about atoms, elements
and chemical reactions.
Fire isn't just fire.
There's no element or chemical substance known as fire.
So what is it?
Well, fire is the name we have given to a visual phenomenon that occurs when matter
burns.
In truth fire is a complex beast and in order to explain exactly what it is, we need to
break it down into it core components.
The first and most important component of fire is the fuel.
This is what's actually burning.
Take a candle for example, the fuel is the wax.
When we set the wick alight the heat causes the molecules in the wax, which are mostly
carbon and hydrogen, to move about erratically.
This causes the covalent chemical bonds which are holding the molecules together, the break
apart.
Releasing individual hydrogen and carbon atoms, as well as hydrogen-carbon molecules.
These individual atoms and molecules form a gas which travels upwards from the candle.
This process is known as Pyrolysis.
The gas travels upwards because of gravity.
The air immediately surrounding the candle flame get's heated up.
The cold air surrounding the hot puts pressure on the hot air, because cold air is more dense
than hot air.
The pressure exerted from the cold air pushes the hot air upwards and the heat rises, as
this happens the cold air replaces the hot air and gets heated up itself.
This process repeats itself for as long as the flame is alight.
This is a process known as convection.
But heat only rises in this fashion in gravity rich environments.
In outer space flames don't travel upwards, they instead radiate in a perfectly spherical
pattern from the source.
So now we have established fire's second component, gas.
The elements that make up the gas in fire depends entirely on the fuel.
If you change the fuel, you also change the properties of the fire.
But there's still two more components to fire, light and heat.
So far we have deduced that fire is mostly gas but gases don't usually give off light,
so where does the light come from.
This is where oxygen comes in.
We all know that oxygen, or some other highly oxygenated substance is required to make a
fire and keep it burning.
So back to the candle, when the gas rises from the candle the atoms in the gas are still
moving around vigorously because of the heat.
These excited, but clumsy, atoms collide with oxygen atoms in the air.
When the two atoms meet they interact with one-another to cause a chemical reaction.
Some of the energy from this reaction gets released as photons of light and so we see
a bright blue, orange, red or white flicker.
This process is known as chemiluminescence.
The remaining atoms that don't collide with oxygen get carried up the flame and eventually
heat up to a level where they give off visible light, this is known as incandescence.
Now imagine billions of these tiny, chemiluminescent and incandescent chemical reactions, producing
billions of tiny little flickers of light, every second - that is what makes a flame
burn so brightly.
The colour of the flame depends of the molecules that make up the fuel and subsequently the
gas which is releases when burned.
The temperature at which it burns also effects the colour.
You can therefore estimate the temperature of a flame based on its colour.
A red flame is anywhere from 525 to 1,000 degrees Celsius.
Orange is between 1,000 and 1,2000 degrees Celsius and at white flame is around 1,500
degrees.
But a blue flame is significantly hotter at around 3,000 degrees Celsius.
And so to the final component of fire, heat.
Why is fire hot?
Well this is really quite simple.
The heat you feel from a flame is just the energy being released from the billions of
chemical reactions occurring between the atoms in the flame and the oxygen in the air.
All chemical reactions either give off energy as a byproduct or absorb energy.
The chemical reactions that happen in a fire are exothermic, which means they give off
energy; as opposed to endothermic which is when a reaction absorbs energy.
So to summarise, what exactly is it you're seeing when you look into a flame?
You're seeing a gas undergoing billions of tiny chemical reactions which are giving off
photons of light and thermal energy.
Oh and you're also looking at millions of tiny diamonds being created and disappearing
right before your eyes.
Yes diamonds, in a flame, the carbon atoms released from the fuel come together to create
diamond nanoparticles, millions of times per second.