Reversible Reactions & Dynamic Equilibrium

 The Haber Process is a REVERSIBLE reaction.  A reversible reaction is one where the products of the reaction can themselves react to produce the original reactants.

 The French chemist Le Chatelier worked all this out!!!  In a dynamic equilibrium the position of the equilibrium will shift in order to relieve any stress you introduce.

Effect of pressure  Any increase in pressure will favor the forward reaction to produce more ammonia (eq. will shift to decrease the pressure of the system)  In terms of the rate of a gas reaction, increasing the pressure brings the molecules closer together, increasing their chances of hitting and sticking to the surface of the catalyst where they can react. 4 molecules of gas 2 molecules of gas

 In the Haber process, the pressure is set as high as possible to give the best % yield.  High pressure containers are VERY expensive.  It could be possible to carry out the reaction at 1000 atmospheres – but this would not be economical (it would cost more than the product is worth).  The typical pressure used is 200 to 300 atmospheres.

 The reaction produces heat when it moves to the right  This mean that running the reaction at a low temperature would favor the forward reaction, BUT…  Reactions go slower at low temperatures!

 In order to get NH 3 produced at a quicker rate the reaction is carried out at a high temperature (450 o C)  It is better to get just a 10% yield in 20 seconds (at a higher temperature) than a 20% yield in 60 seconds at a low temperature.

 Haber sought a “balance” and discovered that an iron(III) oxide CATALYST allowed the equilibrium position to move quickly to the right.  Catalyst lowers the activation energy so the N 2 bonds and H 2 can be more readily broken.

 It took over 6500 experiments at different temperatures and pressures carried out by the German, Carl Bosch to work all this out.  He got a Nobel Prize for it in 1931  Haber got his Nobel Prize in 1918

Schematic of Conditions

 At each pass through the reactor, only about 15% of the reactants are converted into products under these conditions, but this is done in a short time period.  Ammonia is cooled an liquefied at the reaction pressure ( o C), and then removed as liquid ammonia. This further pushes the reaction to the right!!  The remaining mix of nitrogen and hydrogen gases (85%) are recycled & fed at the reactant stage.  The process operates continuously and the overall conversion is about 98%.

 Nitric Acid  Ammonium nitrate (& other salts) ~fertilizers and explosives  Fibers & Plastics (nylon)  Pharmaceuticals (B vitamins, nicotinamide & thiamine)  Cleaning Products  Mining & Metallurgy  Pulp & paper

 Fritz Haber, German chemist,  Winner of the Nobel Prize for Chemistry (1918) for the synthesis of ammonia from its elements.  Carl Bosch developed the industrial stages for the Haber process. The perfection of the Haber-Bosch process encouraged Germany to enter World War I.  Father of Chemical Warfare?  Haber perhaps served his country in the greatest capacity. Without his process and its applications, Germany would never have had a chance to win the war. (World War I)  During the war, Haber led the chemical war and headed the first attack with chlorine gas in Ypres (1915).  Later on, Hitler’s regime ordered his exile due to his Jewish origins.