For the synthesis of ammonia

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

Problem

For the synthesis of ammonia,

N_2(g) + 3\,H_2(g) \rightleftharpoons 2\,NH_3(g)

\Delta H^\circ = -92\,\text{kJ mol}^{-1}

the equilibrium constant in terms of partial pressures is

K_p = 4.34\times10^{-3}

500\,\text{K}

. A sealed

10.0\,\text{L}

vessel at

500\,\text{K}

initially contains

N_2

2.00\,\text{atm}

H_2

6.00\,\text{atm}

, and no

NH_3

. Respond to the following prompts. Assume ideal-gas behavior. (a) Write the expression for

K_p

for the reaction. (b) Calculate the equilibrium partial pressures of

N_2

H_2

, and

NH_3

500\,\text{K}

. (c) Determine the percentage of the initial nitrogen that has been converted to ammonia at equilibrium under the conditions in part (b). (d) The contents of the vessel in part (b) are now compressed isothermally so that the total pressure immediately doubles (before any shift in equilibrium occurs). Without performing a second ICE table, predict whether the equilibrium amount of

NH_3

will increase, decrease, or remain unchanged after the system re-establishes equilibrium. Justify your prediction qualitatively.

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