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Old Dec 27th 2017, 12:46 PM   #1
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Question Partial pressure and Gibbs free energy

Hi everyone,

i'm given the equation in the red zone in my attempt:
NH4Cl<=>NH3+HCl at a temperature of 298K. I have to calculate what the partial pressure of HCl will be at the equilibrium of this reaction, starting only with NH4Cl in an closed room. In order to do this, I have to first calculate the Gibbs free energy (using thermodynamic tables for enthalpy and entropy values), which I do in the green zone. After that I can use this value and the given temperature to calculate the Kp (partial pressure equilibrium constant). NH4Cl doesn't appear in this one because it's in the solid phase, while the other two in the gaseous phase. After that, the only way I found to isolate the partial pressure of HCl, was to assume that, as the reaction starts with no products, the amount of NH3 and HCl at aquilibrium would be equal, and thus their partial pressures too (in the purple zone). Apparently this wasn't the right way of thinking or I made a mistake somewhere, because the correct answer given by my course is 9.34*10^-9bar.

Can anyone help me?

Thanks in advance
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equilibrium constant, gases, partial pressure, thermodynamics

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