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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: laddoo12 on January 31, 2012, 11:23:33 PM

Title: Need some quick question help
Post by: laddoo12 on January 31, 2012, 11:23:33 PM

Solid compound A decomposes according to the endothermic reaction:
A(s)-->2B(g) + C(g) Kp = 1.08 x 10-4

a) If 50.0 mmol of A(s) is placed in a 6.10-L sealed, evacuated flask at 25°C, calculate the total pressure in the flask at equilibrium.

well i plugged all these into the Pv=nRt formula

P=0.05mol(0.08206)(298K)/6.1L   and i get the wrong answer for the pressure
the answer is 9.0x10^-2 Atm how would i get there :S please help thanks !

Title: Re: Need some quick question help
Post by: UG on February 01, 2012, 12:21:02 AM

Can you write the equilibrium expression for this reaction? Note that A is a solid so it doesn't appear in this expression. All you need is this expression and some algebra to do the rest. Think about the ratio of B and C, then can you substitute some variable 'x' representing the partial pressure of C into the equilibrium expression? And then write the partial pressure of B in terms of 'x'? Hope this helps, but do get back if you are still stuck