[BluePill]

So here's the problem:

For the reaction 2NO_2(g)   2NO_g + O_2(g),  Kp = 6.76 x 10^-5 for pressure in atm at 184^oC. Calculate the degree of dissociation when the equilibrium pressure is (i) 1 atm and (ii) 2 atm.

My solution was this:



My answer for (i) 0.05 (ii) 0.04 but the correct answer is (i) 0.0256 and (ii) 0.01995.

What am I missing?

[Jorriss]

As far as I can reason, the way you wrote your ICE table is not quite right.

It needs to be -2a,+2a and +a. Yours is proportionately right but off by a factor of two.

On another note, it says the equilibrium pressure is 1 atm, why did you set the reactant starting amount to 1 atm?

[BluePill]

In the ICE table, I used the mole concept.

[Jorriss]

In the ICE table, I used the mole concept.

I know... but it's off by a factor of two.

[BluePill]

Now I got your point. Thanks.

[BluePill]

But why is that the case? I mean it is just proportionally the same.

[Jorriss]

But not everything is about proportions.

If you have 1 mole of reactant and it loses .5 moles and .5 moles of product are made, this is different than losing .25 mole and making .25 mole of product.