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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: cloudy1290 on June 22, 2019, 10:28:25 AM

Title: How to calcuate this Equilibrium Calculation question?
Post by: cloudy1290 on June 22, 2019, 10:28:25 AM
Given moles of H2 = 3 mol, moles of N2 = 9 mol for equation, 3H2 + N2 --> 2NH3, and the container containing both of them has 3L of volume

after Equilibrium NH3 gives 50% mole fraction(Means that after reaction is complete, the number of moles of NH3 formed from reaction occupies 50% of the total number of moles of all gases in the container) , the total volume of H2 and N2 in container before reaction is 3L.

1. Find mole of H2, N2 and NH3 after equilibrium
2. Calculate the heat. Given that delta H = -91 kJ
3. Calculate K
my solution :

  3H2 + N2 ----> 2NH3

I   3      9

C -3x    -x           +2x

E 3-3x  9-x           2x

then 2x/(2x+12−3x−x) = 1/2 then x = 2

but it's impossible because moles of H2 after equilibrium will be -3

so what's my mistake?
Title: Re: How to calcuate this Equilibrium Calculation question?
Post by: AWK on June 22, 2019, 10:35:58 AM
Equilibrium equation should contain some powers.
Title: Re: How to calcuate this Equilibrium Calculation question?
Post by: cloudy1290 on June 22, 2019, 10:51:13 AM
Quote from: AWK on June 22, 2019, 10:35:58 AM
Equilibrium equation should contain some powers.

power?
Title: Re: How to calcuate this Equilibrium Calculation question?
Post by: AWK on June 22, 2019, 01:04:28 PM
Write down a general equilibrium equation. It should be a cubic one.
Title: Re: How to calcuate this Equilibrium Calculation question?
Post by: cloudy1290 on June 22, 2019, 01:10:27 PM
Quote from: AWK on June 22, 2019, 01:04:28 PM
Write down a general equilibrium equation. It should be a cubic one.

K = [NH3]^2 / [H2]^3*[N2]^3  ?

TBH, i don't understand
Title: Re: How to calcuate this Equilibrium Calculation question?
Post by: AWK on June 22, 2019, 01:27:16 PM
 example
Title: Re: How to calcuate this Equilibrium Calculation question?
Post by: cloudy1290 on June 22, 2019, 01:43:08 PM
Quote from: AWK on June 22, 2019, 01:27:16 PM
example

So it becomes K = 4x^2 / 27(x-9)(x-1)^3 then?
Title: Re: How to calcuate this Equilibrium Calculation question?
Post by: AWK on June 22, 2019, 05:39:06 PM
Now nothing can be calculated since your numerical data are wrong.
Quote
Given moles of H2 = 3 mol, moles of N2 = 9 mol for equation, 3H2 + N2 --> 2NH3

Assuming complete reaction for hydrogen: 8 moles of N2 is left and 2 moles of NH3 are formed.
It means that the maximum number of moles of ammonia equal to 20 % moles of all gases after the reaction.

Quote
the number of moles of NH3 formed from reaction occupies 50% of the total number of moles of all gases in the container
Title: Re: How to calcuate this Equilibrium Calculation question?
Post by: cloudy1290 on June 22, 2019, 06:04:12 PM
I see, but how to calculate question 2 ; Calculate the heat. Given that delta H = -91 kJ. Could you tell me the method in case data is right