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Equilbria Kc Question

Hi,

So the question is as follows:

4. For each of the following calculate the Kc
value and give its units:
(a) This question is about the reaction: N2
O4
(g) 2NO2
(g)
0.4 moles of N2
O4
is allowed to decompose. At equilibrium there
is found to be 0.1 mole of N2
O4
in the 0.5 dm3
gaseous mixture.

Sory for the typo,before hand.

How would you go on about approaching this question?

I am a bit confused about the ICE Method applied here.

Any help, will highly be appreciated from anyone who manages to solve this with a proper explanation.

Thanks.

Reply 1

charco

Study Forum Helper

Original post by Anisha23456789

Hi,

So the question is as follows:

4. For each of the following calculate the Kc
value and give its units:
(a) This question is about the reaction: N₂O₄ <==> (g) 2NO₂(g)

0.4 moles of N₂O₄ is allowed to decompose. At equilibrium thereis found to be 0.1 mole of N₂O₄
in the 0.5 dm3 gaseous mixture.

Sory for the typo,before hand.

How would you go on about approaching this question?

I am a bit confused about the ICE Method applied here.

Any help, will highly be appreciated from anyone who manages to solve this with a proper explanation.

Thanks.

You know the initial moles of N₂O₄, AND you know the moles of N₂O₄ at equilibrium, therefore you know how many moles have reacted.

Armed with this information you can work out the moles of NO₂.

Then mol/vol = concentration

Then work out kc

Reply 2

Anisha23456789

Original post by charco

Right.....so the change in moles for 2n02 is going to be 0.3 moles? And for n204 its going to be 0.1 moles?

Reply 3

charco

Study Forum Helper

Original post by Anisha23456789

Right.....so the change in moles for 2n02 is going to be 0.3 moles? And for n204 its going to be 0.1 moles?

You don't want the change in 2NO₂, you need the change in NO₂

Which will, of course, be twice as large ...

Reply 4

username4793362

n=cxv > work out concentration , rearrange

Reply 5

Anisha23456789

Im still confused....can someone provide a detailed explanation?

Reply 6

charco

Study Forum Helper

Original post by Anisha23456789

Im still confused....can someone provide a detailed explanation?

You know the initial moles of N₂O₄, AND you know the moles of N₂O₄ at equilibrium, therefore you know how many moles have reacted.

Moles of N₂O₄ reacted = 0.4 - 0.1 = 0.3

Acording to the equation 1 mol of N₂O₄ makes 2 mol of NO₂ therefore final moles of NO₂ = 2 x 0.3 = 0.6 mol

Now you have to divide all of the moles by 0.5 to get the concentrations and substitute the values in the kc expression:

Kc = [NO₂]²/[N₂O₄] = (1.2 x 1.2)/0.2 = 7.2