[Cooper]

UPDATE: FIGURED IT OUT, THANKS ANYWAY.

Hi,

Q. At 2257k and 1 bar total pressure, water is 1.77 per cent dissociated at equilibrium by way of the reaction [tex]2H_2O(g)\rightleftharpoons 2H_2(g)+O_2(g)[/tex]Calculate K.

I began by making an ICE table, and I said the change in water to equilibrium was [tex]n-2\alpha n[/tex] where n is an arbitrary amount of water and alpha is the degree of dissociation. I ended up getting the wrong answer. I noticed my answer key says the change in water to equilibrium was [tex]n-\alpha n[/tex]. Attached is a picture of the answer key (see below). I get in the ICE table, they acted as if they were using the equation [tex]H_2O(g)\rightleftharpoons H_2(g)+\frac{1}{2}O_2(g)[/tex], but I don't get why this is necessary. I just used the original equation. Additionally, if they are going to base their ICE table off that reaction, why do they use a water coefficient of 2 when calculating K?

Thanks

[Cooper]

Answer key.

[Cooper]

In case anyone is confused in the future...

The degree of association applies to water, and since oxygen is being made at half the rate water is splitting, it only has a coefficient of 1/2 in the ICE table. However, since the water still has a coefficient of 1 in the reaction, you still need to use a 2 when finding the K value.