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  • 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.

What would you say

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B2 TED-Ed nitrogen ammonia hydrogen equilibrium chemical

【TED-Ed】The Haber process - Daniel D. Dulek

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    稲葉白兎 posted on 2015/01/17
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