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# Calculating Kp watch

1. (Original post by Tuffyandtab)
I agree i think but I haven't done this topic before so bare with (I'm going onto 2nd year a level chemistry).
n2 + 3h2 --> 2nh3
mole fraction of nh3 = 0.15
mole fraction of n2 = 0.25 - (0.15/4) = 0.2125
mole fraction of h2 = 0.75 - 3(0.15/4) = 0.6375
Pa of nh3 = 1500
Pa of n2 = 2125
Pa of h2 = 6375
Kp = (1500)^2/(2125) x (6375)^3 = 4.08679653e-9 I hope this helps. Happy to explain
I think I got that but the answer is 0.99 close to 1. Thanks anyway
2. (Original post by coconut64)
But that question only gives you the partial pressure whereas the question I'm doing now gives you hints about the inital moles and moles at equilibrium here is the explanation
(Original post by coconut64)
I have actually done that already but I don't know how to work out the mole of ammonia so my equilibrium moles for the reactants are wrong. If I am using the values 0.25 and 0.75 for my 1:3 ratio, it wouldn't work as 3/2 of 0.9 is 1.35
Yeah I have no idea how they got to that answer.

Just to check I'm not being silly, is it just me or does their reaction mixture at equilibrium contain 29% ammonia? 0.9/3.1 is definitely not 15%.
3. (Original post by alow)
Yeah I have no idea how they got to that answer.

Just to check I'm not being silly, is it just me or does their reaction mixture at equilibrium contain 29% ammonia? 0.9/3.1 is definitely not 15%.
Yeah I think that explanation is wrong. At one point it says the total equilibrium moles is 6 and then at the end they say it's 3.1!
4. (Original post by alow)
Yeah I have no idea how they got to that answer.

Just to check I'm not being silly, is it just me or does their reaction mixture at equilibrium contain 29% ammonia? 0.9/3.1 is definitely not 15%.
I don't really understand it but I thought 0.9 is 15% of 6 instead of 3.1? I guess the problem lays within the values I use, I think only 1 and 3 will work. Thanks though
5. (Original post by coconut64)
I don't really understand it but I thought 0.9 is 15% of 6 instead of 3.1? I guess the problem lays within the values I use, I think only 1 and 3 will work. Thanks though

Can I just say that the mole fraction for nh3 must be 0.15 as it's 15%. Are you sure 0.99 is the answer? I'm pretty sure that explanation in the red text is wrong.
6. (Original post by Tuffyandtab)
Can I just say that the mole fraction for nh3 must be 0.15 as it's 15%. Are you sure 0.99 is the answer? I'm pretty sure that explanation in the red text is wrong.
Opps , the answer is 3.156 x 10-3kPa-2, I didn't scroll down
7. (Original post by alow)
Yeah I have no idea how they got to that answer.

Just to check I'm not being silly, is it just me or does their reaction mixture at equilibrium contain 29% ammonia? 0.9/3.1 is definitely not 15%.

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