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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: roseandmirrors on July 06, 2019, 02:53:12 PM

Title: equilibrium constant question
Post by: roseandmirrors on July 06, 2019, 02:53:12 PM
The question : Contain SO2 1 mole, O2 2 moles, SO3 0.5 mol in a close system size 5.0 dm3
Which occurs this reaction 2SO2​ + O2 ::equil:: 2SO3 when the system is in equilibrium state, there are SO3 40% by moles. Find out equilibrium constant (k)

I try to solve it :
[SO2] = 1 ÷ 5 = 0.2 M
[O2]​ = 2 ÷ 5 = 0.4 M
[SO3]​ = 0.5 ÷ 5 = 0.1 M

SO3 40% by mole = (1 + 2 + 0.5) × 40% = 1.4 mole
[SO3]​ = 1.4 ÷ 5 = 0.28 M

so..
[SO3] :rarrow: 0.1 + 0.18 = 0.28 M
[SO2]​ :rarrow: 0.2 - 0.18 = 0.02 M
[O2]​ :rarrow: 0.4 - 0.09 = 0.31 M

k = [SO3]​2 ÷ [So2]​2[O2]
  ​ = (0.28)​2 ÷ (0.02)2(0.31) = 652.26

but my key book said that the answer is 76.9, what is wrong with my way to solve this question?
Title: Re: equilibrium constant question
Post by: AWK on July 06, 2019, 03:20:21 PM
Quote
when the system is in equilibrium state, there are SO3 40% by moles
check oxygen in equlibrium!
Title: Re: equilibrium constant question
Post by: roseandmirrors on July 06, 2019, 04:21:16 PM
I'm afraid that I still didn't quite get it but thank you so much, I'll try to think about this again in the morning
Title: Re: equilibrium constant question
Post by: AWK on July 06, 2019, 04:26:09 PM
Quote
40% by mole = (1 + 2 + 0.5) × 40% = 1.4 mole
less than 2 moles
Title: Re: equilibrium constant question
Post by: roseandmirrors on July 06, 2019, 05:06:50 PM
I understand it now. Thank you so much. You are life saver. 🙏