Question

The scenario The conversion of ammonia to hydrogen and nitrogen is not very efficient, even though it's only weakly endothermic (~11 kJ/mol). The addition of a solid metal catalyst can speed up the reaction. The rate law for the decomposition of ammonia is expected to be zero order with these metals at relatively low pressure and high temperatures. For example, on solid platinum the rate law is Rate = k[NH3]° = k. As the total pressure increases, however, the reaction kinetics change. At high pressure, the law becomes Rate = k[NH3] [H2] (or Rate = k*[NH3]/[Hz]). Using your chemical knowledge, explain and/or demonstrate • what the rate laws tell you about the chemistry why the rate law would change at higher pressures the role of the catalyst in the different rate law • how you could increase the reaction rate n this scenario

Answer 1

1) The Rate Law tells that The Reaction isn't feasible at High Pressure. Because, the Rate Law contains [H_{​​​​​​2}] term in the Denominator, which means that at High Pressure, instead of Decomposition, Ammonia Is formed from Nitrogen and Hydrogen.

2) The Rate Law would change at Higher Pressure, because at High Pressure, the Equilibrium Shifts towards the Ammonia, to lower the Volume of the System, according to Le-Chatelier's principle. Thus, at Higher Pressure, the Rate Law is changed.

3) The Catalyst complexes with Ammonia, and lowers the Activation Energy of the Reaction. Thus, the Active Reactant is the Metal-Ammonia Complex, and Hence, the Rate doesn't depend on the Concentration of Ammonia, at low pressure, because the Equilibrium shifts towards the Forward Direction, at low pressure.

4) In this scenario, we have to remove the Nitrogen and Hydrogen Formed, to shift the Equilibrium towards the Forward Direction. Thus, the Rate of the Reaction would be Increased.