The Haber-Bosch Process

The Machine

Machine

Haber's equation and ideas were simple enough, but he needed to find a way to maximize his ammonia production. He built a machine (using Le Chatelier's principle, more on this later) to shift equilibrium as far toward the products as possible in order to maximize ammonia output while maintaining a fast reaction rate. This is a schematic diagram of his machine:

Iron-Based Catalyst

Catalyst

The iron-based catalyst serves to lower the activation energy of the reaction. It allows the reaction to use a lower-energy pathway, allowing for more efficiency. The original and catalyzed energy diagrams look like this:

**Note that this delta H (which should be - to denote exothermic) is at 298 K, NOT typical reaction temperature.

Reaction Rates

Reaction Rates

The higher the temperature, the faster a reaction will proceed. Thus, the reaction is typically carried out around 673-723 K in order to produce ammonia as quickly as possible. Although this is a high temperature, it is not higher due to considerations with respect to Le Chatelier's principle (next slide).

Le Chatelier's Principle

N (g)+3H (g) <--> 2NH (g)

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H = -92.4 kJ/mol

In this reaction, both temperature and pressure must be considered with respect to Le Chatelier's Principle.

Le Chatelier's Principle

Temperature:

This reaction is exothermic. When T increases, the value of K decreases, and the reaction shifts towards reactants, producing less ammonia. 673-723 K is a compromise of reaction rate and ammonia production.

Pressure:

According to Le Chatelier's Principle, when pressure is increased, the reaction shifts towards the side with less moles of gas, creating more ammonia. Thus, this reaction is carried out at 200 atm to maximize ammonia production.

Why is it so important?

Importance

The Haber-Bosch process turns two common air components (nitrogen and hydrogen) into crop fertilizer. Without ammonia to fertilize crops, farmers could only grow enough food to feed about 4 billion people (Dulek). Current estimates put Earth's population at 7.78 billion (World Population Clock), meaning that, without this process, about 48.6% of the world's population would be without food.

Environmental Effects

Environment

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About 290 billion pounds of ammonia are produced every year, and about 80% of the NH is used as fertilizer. However, it has been shown that nearly 50% of the fertilizer used is not absorbed by plants. Not only is that a wasteful excess in production, but it causes dangerous nitrogen compounds to appear in important fresh water supplies, as well as the atmosphere.

Energy/Environment

Energy

As previously stated, 290 billion pounds of ammonia are produced yearly. However, given the conditions required to create ammonia (high temperature and pressure), a lot of energy is required to run the machines. This is both financially costly and environmentally costly, as the machines release greenhouse gases (mostly CO ). Some estimates state that for every ammonia molecule produced, a CO molecule is produced. Scientists are trying to find a new chemical reaction to produce fertilizer without such great harm to the environment.

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