Case Study: The Haber Process:
Ammonia for Food and Bombs
From: Eros Wang
To: Ms. Irumekhai
Date: March 30, 2012
1. Suggest five factors that could affect the production of ammonia in the Haber process. Explain the effect of each factor, using rate theory.
The Haber process itself is a delicate balancing act because of all the factors that affect the yield of ammonia. In the Haber process, the nitrogen, hydrogen and ammonia are in equilibrium. So five factors that affect the production of ammonia would be: a) Temperature. The reaction is an exothermic reaction, meaning it produces heat. The higher the temperature in the reaction chamber, the less ammonia is produced, as the equilibrium shifts to the right to counteract the heat as it is an exothermic reaction, producing more hydrogen and nitrogen gas. But this doesn’t mean that the rate of reaction will be slower. In general, increasing the temperature always increases the rate of reaction. b) Pressure. If the pressure of the system is increased, the hydrogen and nitrogen gas molecules are compressed together, and the equilibrium shifts to the right, forming ammonia molecules. Increased pressure also increases the reaction rate, as the gas molecules are more concentrated and closer together. c) Catalyst. To increase the rate of reaction, a catalyst is used. In the Haber process, the catalyst used is a finely ground porous iron powder, with a large surface area. It absorbs the nitrogen and hydrogen gases and they react with each other on the catalyst’s surface, producing ammonia. d) Concentration of the reactants. Increasing the concentration of the reactants means the equilibrium shifts to the right producing more ammonia gases. By increasing the concentration of the reactants also means that collisions are suddenly much more frequent for the forward reaction. This increases the forward rate significantly. e) Removing the product. If the product (ammonia) is removed, causing the equilibrium shifts to right to producing more ammonia. However, the rate of reaction will still remain the same.
2. Create a concept map starting with “Haber process” and including at least two end uses of the product of this process. [pic]
3. Why is a low temperature, which gives a higher percentage yield of ammonia, not used in the Haber process? The temperature in the Haber process is really a compromise. Since the forward reaction is an exothermic reaction, according to Le Chatelier's Principle, if we lower the temperature, the equilibrium will shift to right to counteract this and producing more ammonia. But the lower the temperature we use, the slower the reaction becomes. A manufacturer is trying to produce as much ammonia as possible per day. It makes no sense to try to achieve an equilibrium mixture which contains a very high proportion of ammonia if it takes several years for the reaction to reach that equilibrium. So a low temperature which gives a higher percentage yield of ammonia is not used in the Haber process.
4. What role does iron oxide play in the Haber process?
Haber discovered that using an iron oxide catalyst eliminates the need for excessively high temperatures, allowing the equilibrium position to move quickly to the right at lower temperatures.
5. a) Determine the most common types of explosives produced with nitric acid. Nitric acid can react violently when mixed with other organic compounds, and for this reason is a major component in some rocket fuels. It is also used in the manufacture of some explosives, such as nitroglycerin and trinitrotoluene (TNT).
b) Draw structural formulas for the three most common nitrogen-based explosives. What are the specific uses of each? Trinitrotoluene (TNT) is often mixed with other explosives such as ammonium nitrate to form amatol. Because it is insensitive to shock and must be exploded with a detonator, it is the most favored explosive used in...