Question

d. The "complete" mechanism of the reaction is shown below (actually, I've simplified it just a bit). Hydrazine (N2Ha) is an intermediate in the reaction pathway, and the reaction consists of two elementary steps. Draw a reaction coordinate diagram that represents the key features of the reaction, including the relative energies of the reactants and products 2 H2 (g)+ N2g) N,H4 (g) (Slow) H2 (g) + N,H82 NH, (g) e. Write the instantaneous rate law for this reaction. f. 100.0 g of nitrogen gas was allowed to react with 25.0 g of hydrogen gas in the reaction above. The actual yield of this reaction was 45.0 g of ammonia produced. What is the % yield? g. What effects would the following perturbations have on the position of the overall reaction's equilibrium? Briefly, explain your reasoning The external pressure is increased . The reaction temperature is raised . A catalyst is added . NH3 (g) is removed from the system h. If Ke for the reaction is 0.453 at 600 K, [H2li 1.00 M, and [N2) 2.00 M what will the molar equilibrium ammonia concentration be? The equilibrium [N2]-0.500 M

Answer 1

d. This reaction is an Exothermic Process i.e. heat is released during the reaction.

Overall reaction can be represented as

  $N_{2}\, + \, 3H_{2}\, \rightleftharpoons \, 2NH_{3}\, \, \, \, \, \Delta \,H^{o}\, =\, -91.8\, kJ/mol$

Therefore reaction coordinate diagram for this is equation is:

Energy N2+ 3H2 AHE-91.8 ku/mol Reaction progress

e. Instantaneous law can be defined as change reactants concentration or of products at any instant time in the reaction.

Instant rate can be calculated using  

3 Instantaneous reaction rate dt

where dA = small change in concentration of a NH₃ (reactant or product)

dt = small change in time at that instant

f. It can be seen from above equation that for 2g of H₂ reacts with 14g of N₂ to produce 51g of NH₃

so comparing with given data for

100g of N₂ = (2/14)*100 of H₂ is required = 14.28g of H₂

therefore N₂ is the limiting reactant

Theoretical yield of above reaction is,

100g of N₂ = (51/14)*100 g of NH₃ = 364.28g of NH₃

%yield = (Actual yield/ Theoretical yield)*100

= (45/364.28)*100 = 12.33%

g. i.  On increasing the external pressure according to Le Chatelier's principle the equilibrium will move towards the right resulting in higher yield of NH₃. Pressure change cause system to adjusts in order to reduce the effect of the change since more number of molecules cause high pressure.

ii. Increase in reaction temperature generally favours endothermic reaction in order to cool system to required temperature therefore this will result in shift of equilibrium towards left side i.e production of NH₃ will decrease.

iii On addition of catalyst in reaction the forward and reverse reaction rate will gradually increase but the concentrations of system remains same therefore equilibrium remains unaffected because of catalyst since catalyst only speeds up the reaction of the system by lowering the activation energy.

iv Reaction will be shift forward i.e.towards right in order to attain equilibrium with all three components, by producing NH₃ molecules all over again.

h. Equilibrium expression of this reaction is

Kc =	[NH3(g)]2      [N2(g)][H2(g)]3

hence using this equation

0.453 = [NH₃]²/ 2

NH₃ = 0.951 M