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Old Sep 17th 2011, 07:24 AM   #1
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Find mass of gas given the partial pressure gas

NH3(g)+HCl(g) <--> NH4Cl(s)

Gaseous ammonia and hydrogen chloride are injected into an evacuated 2dm^3 vessel that is maintained at 300 degree Celsius. more NH3 is then injected into the vessel such that the amt of ammonia exceeds the HCL. White crystals of NH4Cl solid are formed. when the system reached equilibrium, the total pressure inside the vessel is 1.086 atm. the numerical value of the equilibrium constant Kp is 17.6

The partial pressure of HCl at the instant of mixing was 0.6 atm. Assuming that the gases behave ideally, calculate the mass of NH4CL in the vessel at equilibrium.

Last edited by grgrsanjay; Sep 17th 2011 at 08:49 AM. Reason: Spelling Errors
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Old Sep 17th 2011, 10:47 AM   #2
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Kp = (P_NH4Cl) / (P_NH3)(P_HCl)

Since a solid does not have a partial pressure, you put (P_NH4Cl) = 1

Use PV = nRT to get the total number of moles of gas at equilibrium.

Let x be the partial pressure decrease of HCl after equilibrium is reached.

0.6-x is the final partial pressure of HCl.

The partial pressure of NH3 is then (1.086 - (0.6-x))

Use the equilibrium constant equation to find the value of x, the partial pressure decrease of HCl.

From the initial and final partial pressure of HCl, find the decrease in number of moles of HCl.

This is the number of moles of NH4Cl too, so now, you can find the mass of NH4Cl.
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Old Sep 30th 2011, 07:34 AM   #3
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mass of gas given partial pressure

Hello helloying,
I researched this dissociation equilibrium on line and think that your question is not from a book or teacher for the following reasons
1 equation is written ammonium chloride s = NH3 g + HCL g
2 Kp is (NH3 ) atm * (HCL) atm partial pressures solid does not show but some amount must be present
3 Kp = 17.6 is incorrect and 1/17.6 is too high for 300 deg C

In case you didn't know the reaction does not proceed in either direction in absence of water catalyst. Given clear descriptions and values there are a couple of ways to find the partial pressures of NH4CL,HCL, NH3.

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