Synthesis of Ammonia: Process & Reaction

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  • 0:04 History of the Haber Process
  • 1:02 The Haber Process
  • 1:36 Obtaining Hydrogen
  • 3:01 Obtaining Nitrogen
  • 4:50 Conditions Needed
  • 6:17 Lesson Summary
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Lesson Transcript
Instructor
Hemnath (Vikash) Seeboo

Taught Science (mainly Chemistry, Physics and Math) at high school level and has a Master's Degree in Education.

Expert Contributor
Christianlly Cena

Christianlly has taught college physics and facilitated laboratory courses. He has a master's degree in Physics and is pursuing his doctorate study.

This lesson helps you to understand how ammonia is synthesized industrially. You'll also learn the conditions that are required for the Haber process to take place.

The History of the Haber Process

Today's industries use the Haber process to synthesize ammonia, but it wasn't invented until the early 20th century.

Back in 1898, Sir William Cook, a British chemist, predicted that part of humanity could be faced with the prospect of starving to death because of lack of nitrogen fertilizer for plant growth. At that time, almost all nitrogen in the soil, as nitrate, was fixed over hundreds of years by microorganisms, and those rich organic soils were rapidly depleting. Already, industrialized countries, like Germany, were relying on animal manure, like guano from South America, to make nitrogen-based fertilizers.

Fortunately, in 1908, a German chemist named Fritz Haber developed a chemical method for producing large amounts of ammonia, using a process that is now known as the Haber process. The ammonia thus produced could be easily converted to nitrogen-based fertilizers. Ammonia is also used to make explosives and cleaning products.

The Haber Process

The Haber process is an industrial process that uses nitrogen gas and hydrogen gas to synthesize ammonia. The equation that represents the Haber process is given by:


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Obtaining Hydrogen

So, how does the process obtain it's hydrogen?

1. Electrolysis of water

You will recall that the passage of an electric current through water using inert electrodes produces hydrogen at the cathode and oxygen at the anode.

2H2 O + Electrical energy --> 2H2 + O2.

It is good to note that this method of obtaining hydrogen for the Haber process was used for the production of ammonia in the 20th century.

2. Reaction of methane and steam

With time, chemists found a comparatively cheaper and more efficient way of producing hydrogen. The method involves using a methane source, such as natural gas, which is reacted with high-temperature steam at 700°C-1,000°C and under 3-25 bar pressure. Alongside hydrogen, carbon monoxide and a relatively small amount of carbon dioxide is formed.

CH4 + H2 O + heat --> CO + 3H2 (+ small amount of CO2)

Subsequently, the carbon monoxide and steam are reacted using nickel as a catalyst to produce carbon dioxide and more hydrogen.

CO + H2 O --> CO2 + H2

Finally, carbon dioxide and other impurities are removed from the gas stream by using a method known as the pressure-swing adsorption. This leaves essentially pure hydrogen behind.

Obtaining Nitrogen

Okay, now how does the process obtain nitrogen?

1. Fractional distillation of liquid air

Nitrogen can be obtained through the fractional distillation of the air around us. Air is compressed down to 200o C. Trace gases, carbon dioxide and water are removed by filtering. Oxygen and nitrogen liquefy at -183o C and -196o C respectively. This liquefied mixture, comprised of oxygen and nitrogen, is then separated by fractional distillation. Since liquid nitrogen boils at a lower temperature than oxygen, it will rise up the fractionating column while liquid oxygen remains at the bottom. However, this method of obtaining nitrogen is too expensive.

2. Reaction of methane and air

Recall that air is made up of around 78% nitrogen, with nearly all the rest being oxygen. If we burn methane in air, the oxygen reacts with the methane to produce carbon dioxide and water. You can understand that the nitrogen present in the air remains unreacted. If we remove the carbon dioxide and water, we obtain nitrogen.


Production of nitrogen and hydrogen
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Additional Activities

Modified True or False Exercise on the Synthesis of Ammonia


Exercise

Check your knowledge in the lesson about the process and reaction in the synthesis of ammonia by determining whether the following statements are true or false. For this activity, print or copy this page on a piece of paper. Write TRUE if the statement is valid and FALSE if otherwise on the blank space provided. If the statement is FALSE, write down the word or phrase that makes it wrong.

_____ 1. A comparatively cheaper and more efficient way of producing hydrogen is by using natural gas.

_____ 2. In a slow temperature, the rate of synthesizing ammonia would be slow and reaching equilibrium requires a much longer time.

_____ 3. In the synthesis of ammonia, oxygen as well as hydrogen is used.

_____ 4. Before the Haber process was developed, industrialized countries like Germany relied on animal manure as fertilizers.

_____ 5. In the Haber process, any unused nitrogen and hydrogen are removed from the reactor.

_____ 6. Pressure-swing adsorption is a method used to remove hydrogen and other impurities from a gas stream.

_____ 7. A catalyst, like nickel, increases the rate of a physical reaction without being consumed by the process.

_____ 8. Le Chatelier's principle states that increasing temperature will favor the side with fewer moles.

_____ 9. The reaction of methane and steam produces carbon dioxide and water.

_____ 10. Ammonia produced through the Haber process could be easily converted to nitrogen-based fertilizers.


Answer Key

For False answers, the correct word or phrase is written in italics next to the incorrect word for comparison.

1. TRUE

2. TRUE

3. FALSE, oxygen, nitrogen

4. TRUE

5. FALSE, removed from, recycled into

6. FALSE, hydrogen, carbon dioxide

7. FALSE, physical, chemical

8. FALSE, temperature, pressure

9. TRUE

10. TRUE

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