The chemical reaction that feeds the world - Daniel D. Dulek

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How do we grow crops quickly enough to feed the Earth's billions? It's called the Haber process, which turns the nitrogen in the air into ammonia, easily converted in soil to the nitrate plants need to survive. Though it has increased food supply worldwide, the Haber process has also taken an unforeseen toll on the environment. Daniel D. Dulek delves into the chemistry and consequences.

Lesson by Daniel D. Dulek, animation by Uphill Downhill.

What would you say

is the most important discovery

made in the past few centuries?

Is it the computer?

The car?

Electricity?

Or maybe the discovery of the atom?

I would argue that it is this chemical reaction:

a nitrogen gas molecule

plus three hydrogen gas molecules

gets you two ammonia gas molecules.

This is the Haber process

of binding nitrogen molecules in the air

to hydrogen molecules,

or turning air into fertilizer.

Without this reaction,

farmers would be capable of producing enough food

for only 4 billion people;

our current population is just over 7 billion people.

So, without the Haber process,

over 3 billion people would be without food.

You see, nitrogen in the form of nitrate, NO3,

is an essential nutrient for plants to survive.

As crops grow, they consume the nitrogen,

removing it from the soil.

The nitrogen can be replenished

through long, natural fertilization processes

like decaying animals,

but humans want to grow food

much faster than that.

Now, here's the frustrating part:

78% of the air is composed of nitrogen,

but crops can't just take nitrogen from the air

because it contains very strong triple bonds,

which crops cannot break.

What Haber did basically

was figure out a way

to take this nitrogen in the air

and put it into the ground.

In 1908, the German chemist Fritz Haber

developed a chemical method

for utilizing the vast supply of nitrogen in the air.

Haber found a method

which took the nitrogen in the air

and bonded it to hydrogen

to form ammonia.

Ammonia can then be injected into the soil,

where it is quickly converted into nitrate.

But if Haber's process was going to be used

to feed the world,

he would need to find a way

to create a lot of this ammonia quickly and easily.

In order to understand

how Haber accomplished this feat,

we need to know something

about chemical equilibrium.

Chemical equilibrium can be achieved

when you have a reaction in a closed container.

For example, let's say you put

hydrogen and nitrogen into a closed container

and allow them to react.

In the beginning of the experiment,

we have a lot of nitrogen and hydrogen,

so the formation of ammonia

proceeds at a high speed.

But as the hydrogen and nitrogen react

and get used up,

the reaction slows down

because there is less nitrogen and hydrogen

in the container.

Eventually, the ammonia molecules reach a point

where they start to decompose

back into the nitrogen and hydrogen.

After a while, the two reactions,

creating and breaking down ammonia,

will reach the same speed.

When these speeds are equal,

we say the reaction has reached equilibrium.

This might sound good, but it's not

when what you want

is to just create a ton of ammonia.

Haber doesn't want the ammonia

to break down at all,

but if you simply leave the reaction

in a closed container,

that's what will happen.

Here's where Henry Le Chatelier,

a French chemist,

can help.

What he found was

that if you take a system in equilibrium

and you add something to it,

like, say, nitrogen,

the system will work

to get back to equilibrium again.

Le Chatelier also found

that if you increase

the amount of pressure on a system,

the system tries to work

to return to the pressure it had.

It's like being in a crowded room.

The more molecules there are,

the more pressure there is.

If we look back at our equation,

we see that on the left-hand side,

there are four molecules on the left

and just two on the right.

So, if we want the room to be less crowded,

and therefore have less pressure,

the system will start

combining nitrogen and hydrogen

to make the more compact ammonia molecules.

Haber realized that in order to make

large amounts of ammonia,

he would have to create a machine

that would continually add nitrogen and hydrogen

while also increasing the pressure

on the equilibrium system,

which is exactly what he did.

Today, ammonia is one of the most produced

chemical compounds in the world.

Roughly 131 million metric tons are produced a year,

which is about 290 billion pounds of ammonia.

That's about the mass

of 30 million African elephants,

weighing roughly 10,000 pounds each.

80% of this ammonia is used in fertilizer production,

while the rest is used

in industrial and household cleaners

and to produce other nitrogen compounds,

such as nitric acid.

Recent studies have found

that half of the nitrogen from these fertilizers

is not assimilated by plants.

Consequently, the nitrogen is found

as a volatile chemical compound

in the Earth's water supplies and atmosphere,

severely damaging our environment.

Of course, Haber did not foresee this problem

when he introduced his invention.

Following his pioneering vision,

scientists today are looking

for a new Haber process of the 21st century,

which will reach the same level of aid

without the dangerous consequences.