Graph of Temperature Versus Equilibrium(Kq) for Ammonia Production

Ammonia is synthesized from nitrogen gas and hydrogen gas in the Haber Process . The equation for its production is given by; 

The forward reaction is exothermic, so, according to the Le Chatelier's Principle  low temperature will favor forward reaction. But Lower temperatures decrease the reaction rates and for maximum yield of ammonia, temperatures between 380 and 450-degree centigrade are used.  

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When you are provided with the following data and you are required to plot a graph of temperature versus equilibrium. Describe the shape of the graph for ammonia production.  What can you predict from the graph?

From the graph, as the temperature increases, the equilibrium drops abruptly according to the Van’t Hoff Equation. Van’t Hoff equation is an equation that shows the relationship among the temperature (T), equilibrium constant (Kq) changes and particular change in standard enthalpy.

The catalyst used in the production of ammonia gives maximum yield when the temperature (at least 400-degree centigrade) is applied. In the graph, equilibrium constant increases as the temperature decreases. To produce the maximum amount of ammonia other parameters (pressure and product removal) must be considered.  

Pressure                                                            

Increasing the amount of pressure favors the forward reaction. In the equation, 4 moles of reactants are consumed to yield two moles of products. Pressures between 200-250 atmospheres are usually applied for maximum production.  Even though, maintaining high pressure is expensive and dangerous, working at 200 atm ensure the process is safe and economical. The high amount of energy applied in running pumps and compressors make the process to produce 15% of ammonia in one pass. 

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Product removal

 Removing ammonia from the system increases its production. Ammonia is removed from the gaseous equilibrium mixture coming out from the reaction vessel. The hot gaseous mixture is cooled promptly to enable ammonia to condense and to be removed in liquid form. The unreacted gasses (nitrogen and hydrogen) are recycled in the process.