A single-pass

CHEMISTRY · Multi-part · A Level · Chemistry · Gaseous equilibria (Kp) · Gaseous equilibria (Kp)

Problem

A single-pass, high-pressure reactor is used for ammonia production:

\mathrm{N_2(g)+3\,H_2(g)}\;\longleftrightarrow\;2\,\mathrm{NH_3(g)}\qquad \Delta H_{rxn} = -92\,\text{kJ mol}^{-1}

At 700 K,

K_p = 6.0\times10^{-5}

. A feed stream containing

\mathrm{N_2}

and

\mathrm{H_2}

in a 1 : 3 mole ratio enters the reactor at a total pressure of 150 atm and negligible ammonia content. Assume ideal-gas behavior throughout. (a) Derive an expression for the initial reaction quotient

Q_p

in terms of the total pressure

P_{tot}

and the stoichiometric mole fractions of the entering gases. Then calculate the numerical value of

Q_p

for the given conditions. (b) Compare the calculated

Q_p

with

K_p

and predict the direction of reaction progress on first entering the reactor. Explain. (c) Plant management is considering increasing the operating pressure to 200 atm while keeping the inlet composition and temperature constant. Evaluate how this change would affect (i) the equilibrium yield of ammonia, (ii) the forward reaction rate, and (iii) economic or safety considerations. Provide a reasoned recommendation on whether the pressure increase should be implemented.

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