Equilibrium law
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I recently came across a question in a past examination paper which did not resemble any of the examples I had previously worked out. The question concerns homogeneous pressure equilibria, specifically the equilibrium reaction of the Haber process, N2(g) + 3H2(g) -> 2NH3(g).
The question read as follows: nitrogen and hydrogen are introduced into a vessel of fixed volume, each of partial pressure 2 atm. The vessel is maintained at 500 K when the gases react to form an equilibrium mixture having a total pressure of 3.6 atm. Estimate the partial pressures of all gases at equilibrium, and deduce a value for Kp for the equilibrium at 500 K.
Any help with shedding some light on how to go about tackling this question would be much appreciated.
130408
Corrie writes ....
Let's say that, at equilibrium, the partial pressure of nitrogen has fallen by X, to 2-X. Then from the balanced equation, it follows that the partial pressure of hydrogen will have dropped by 3X, to 2-3X. It also follows that the partial pressure of ammonia at equilibrium will be 2X, because 1 mol of nitrogen forms 2 moles of ammonia.
Thus the total pressure at equilibrium is (2-X) + (2-3X) + 2X = 3.6. Solve for X. Then work out all the partial pressures (make sure they add up to 3.6) and subsitute them in the formula for Kp.
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updated: 13 April 2008
