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Offline KalEl

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Equilibria Problems
« on: April 28, 2009, 07:54:44 AM »
Greetings  :)

My current chemistry course covers the majority of subjects in detail apart from chemical equilibria which is only touched on slightly so I'm having trouble with these.

The answers to these problems are not needed just the method of working them out, thanks.


Q.1 - In the equilibrium:

N2O4(g) <----> 2NO2(g)


3.20g of dinitrogen tetroxide occupy a volume 1.00 dm3 at 1.00 x 105 Pa and 25C.

Calculate: a) the degree of dissociation, and b) the equilibrium constant


Q.2 Sulphur dichloride dioxide has an apparent molar mass of 75 g mol-1 at 400C and a pressure of 105 N m-2. Calculate the equilibrium constant at 400C for the reaction:

SO2Cl2(g) <----> SO2(g) + Cl2(g)


Thanks in advance guys :)
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Offline AWK

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Re: Equilibria Problems
« Reply #1 on: April 28, 2009, 08:03:45 AM »
Show your attempt!
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Offline KalEl

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Re: Equilibria Problems
« Reply #2 on: April 28, 2009, 11:42:28 AM »
The problem is in order to calculate KP I need to find the degree of dissociation. But to calculate the degree of dissociation I need to find the experimental molar mass which I've indicated with a question mark. How do I find the experimental molar mass?




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Offline sjb

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Re: Equilibria Problems
« Reply #3 on: April 28, 2009, 12:01:21 PM »
Quote from: KalEl on April 28, 2009, 11:42:28 AM
How do I find the experimental molar mass?

It's perhaps worded a little strangely, but...

Quote from: KalEl on April 28, 2009, 07:54:44 AM
Q.1 - In the equilibrium:

N2O4(g) ::equil:: 2NO2(g)


3.20g of dinitrogen tetroxide occupy a volume 1.00 dm3 at 1.00 x 105 Pa and 25C.

Calculate: a) the degree of dissociation, and b) the equilibrium constant

here you have a mass, and a volume, temperature and pressure. You can use a variant of the ideal gas equation to calculate the number of moles using the last 3 data points, and then from that and the mass of gas calculate an effective molar mass.
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Offline KalEl

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Re: Equilibria Problems
« Reply #4 on: April 28, 2009, 02:20:53 PM »
My tutor wants me to show my full method using the degree of dissociation  ::). I've sorted question 2 and got a value 1.78 x 105 N m-2 which, according to the answer book is correct.
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Offline sjb

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Re: Equilibria Problems
« Reply #5 on: April 28, 2009, 03:10:24 PM »
How many moles of gas are there in your mixture? pV / RT = n?

What's the experimental molecular mass of the gas? mass of sample / number of moles = experimental molar mass.

Plug this value into your equation in Q1 and I think you're away...
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Offline KalEl

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Re: Equilibria Problems
« Reply #6 on: April 28, 2009, 03:25:36 PM »
Quote from: sjb on April 28, 2009, 03:10:24 PM
How many moles of gas are there in your mixture? pV / RT = n?

Of course, I can't believe I forgot to use the ideal gas equation  ::)

Thanks for everybody's help, much appreciated :)
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