Question

Ammonia is produced by the catalytic reaction of nitrogen and hydrogen.

A)   Write the chemical reaction and balance it. Determine the stoichiometric coefficients.

B)    If 15 mol/sec of H₂ is fed to the reactor, determine the amount of N₂ required if a 20.% excess (of N₂) is desired.

C)    If 5.0 mol/sec of H₂ exits the catalytic reactor, determine:

i)   ξ.

ii)   the number of moles of all three components exiting the reactor.

iii)   the conversion of H₂ and N₂.

iv)   the exiting concentration of H₂, N₂, and ammonia.

D)   What are strategies to increase the conversion of H₂?

Answer 1

a) Balanced Reaction

N₂ + 3H₂ -> 2NH₃

b) Moles of N₂ with excess

15 mol/s are fed of H_2. By stoichiometry, we can determine how many theoretical moles of N₂ we need:

15 mol/s of H₂ * (1 mol of N₂ / 3 moles of H₂) = 5 mol/s of N₂

5 mol/s of N₂ * 1.2 = 6 mol/s of N₂

c) Moles reacted 15 - 5 mol/s = 10 mol/s of H₂

i) To get the extent of reaction, we divide it by stoichiometric coefficient:

10 mol/s of H₂ / 3 = 3.3333 mol/s

Extent of reaction = 3.333 mol/s

ii) Moles exiting the reactor:

Moles of NH₃ = 3.3333 * 2 = 6.6666 mol/s

Moles of H₂ = 5 mol/s

Moles of N₂ = 6 - 3.3333 = 2.6667 mol/s

iii) Conversion of H₂= moles reacted / moles fed = 10/15 * 100= 66.667%

Conversion of N₂= moles reacted / moles fed = 3.3333/6 * 100= 55.55%

iv) Exiting concentrations:

Total moles = 6.666 + 5 + 2.6667 = 14.3327

%N₂ = 2.6667/14.3327 * 100 = 18.6%

%H₂ = 5/14.3327 * 100 = 34.885%

%NH₃ = 6.666 / 14.3327 * 100 = 46.51%

d) Strategies to increase conversion:

Apply le chatelier principle to shift equilibrium. One of the measures that could be taken is to add more reactants to shift equilibrium to the right. Also, pressure could be increased to reduce volume and so make the reaction produce more ammonia. Finally, temperature should be managed so that equilibrium could be shifted to the right and a good constant is obtianed as well.