Understanding Limiting Reagents and Pressure Calculations in Gas Reactions

[Lancelot59]

NH_3(g) + HCl_(g) --> NH₄Cl_(s)

A 2.00 L flask containing 5.00 g of NH₃ is connected to a 2.00 L flask containing 5.00 g of HCl. When the stopcock between the two flasks is opened the gases react until one of them is completely consumed. What is the final pressure in the apparatus when the reaction is complete? The temperature of the system is 25^oC.

Well I found that HCl was the limiting reagent. I figured that since the equation is a 1:1 ratio I could just set the mols of NH₄Cl as the mols of HCl and solve for the pressure using the ideal gas law.

Apparently there is another step, where I have to subract the mols of the two gasses, and then use THAT value in the gas law.

What is going on here? How is that value the number of mols in the NH₄Cl?

 

[Borek]

NH₄Cl(s). Its volume is so small that it doesn't count.

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[Lancelot59]

I see now. Thanks. Wish me luck on the test today.

I really should've studied more. My other courses drove this test out of my head entirely.
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