Posted by **Chemmy** on Wednesday, March 2, 2011 at 8:44pm.

One mole of N2 and three moles of H2 are placed in a flask at 375 C. Calculate the total pressure of the system at equilibrium if the mole fraction of NH3 is 0.21. The Kp for the reaction is 4.31*10^4.

I assume this to be the reaction

N2 + 3H2 --> 2NH3

Help ?

Forgot to mention: Final answer is 50 atm

- Chemistry -
**DrBob222**, Thursday, March 3, 2011 at 1:48am
...............N2 + 3H2 ==> 2NH3

begin (mols)..1.0...3.0......0

change.........-x.....-3x.....2x

final........1.0-x..3-3x.....2x

total n = 1.0-x+3-3x+2x = 4-2x

And we know mol fraction NH3 = 0.21; therefore,

(2x)/(4-2x) = 0.21 and solve for x = moles.

Use x to determine moles NH3, moles H2 and moles N2 at equilibrium.

Then determine mole fraction N2, NH3(which you have) and H2.

PNH3 = 0.21*Ptotal

PH2 = XH2*Ptotal

PN2 = XN2*Ptotal

Then substitute partial pressures into Kp expression and solve for P. By the way, I think Kp is too large; in fact, I suspect it should be 10^-4 and not 10^4; i.e., I think you made a typo.

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