CHEMISTRY

Chemistry

Chemistry

In the early 1900's, a chemist named Fritz Haber developed a laboratory procedure to form ammonia, the process which now bears his name. The Haber process involves the reacting of nitrogen and hydrogen in temperatures of about 550 degrees Celsius and pressure of 355 atm, using an iron catalyst, to form ammonia. The equation is shown below:

3H2 (g) + N2 (g) 2NH3 (g)

In his original experiment, Fritz Haber obtained hydrogen by decomposing steam over hot coals and nitrogen from liquefied air. Carl Bosch developed Haber's experiment into an industrial size process, using methane instead of steam, and obtaining nitrogen through fractional distillation of liquid air. The process takes place in a large reaction chamber and the remaining reactants are cycled through the process again, while the product, ammonia is liquefied and drained away. (Stephenson 2009:13-20)

The yield of Ammonia in the Haber process is reduced at higher temperatures due to Le Chatelier's Principle. Le Chatelier's Principle states that “The equilibrium position will respond to oppose a change in the reaction conditions”. This means an equilibrium will change accordingly if the total pressure of the reaction is increased or decreased, or if more product or reactant is added, or if the temperature of the reaction

is changed. In the Haber process, the nitrogen, hydrogen and ammonia are in equilibrium. The reaction is also 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.

The Haber process itself is a delicate balancing act because of all the factors that affect the yield of ammonia. These include the reaction energy of the reactant, the reaction rate and the resulting equilibrium conditions. The reaction energy is the amount of energy needed to synthesize the hydrogen and nitrogen gas together to form ammonia. This is achieved by raising the temperature of the reaction, shifting the equilibrium to the left and producing the ammonia product. However, if the temperature is raised too high, the equilibrium will shift and the ammonia will decompose back into the reactants of hydrogen and nitrogen. The reaction rate is the time it takes for the reactants to form the product. This is also increased by increasing the temperature of the reaction and by the use of a catalyst, but again, if it is raised too high the equilibrium will shift and the ammonia will decompose into the reactants. (Pauling 2006:77-56)

To increase the rate of reaction, a catalyst is used. In the Haber process, the catalyst used is a finely ground porous iron powder (usually Fe3O4), 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.

If the pressure of the system is increased, the hydrogen and nitrogen gas molecules are compressed together, and the equilibrium shifts to the left, forming ammonia ...