6th Edition 11.89

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Hai-Lin Yeh 1J
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6th Edition 11.89

Postby Hai-Lin Yeh 1J » Mon Jan 14, 2019 2:51 pm

The following plot shows how the partial pressures of reactant and products vary with time for the decomposition of compound A into compounds B and C. All three compounds are gases. Use this plot to do the following: (a) Write a balanced chemical equation for the reaction. (b) Calculate the equilibrium constant for the reaction.
Screen Shot 2019-01-14 at 2.50.04 PM.png

I already understand how to do A and the balanced equation should be 2A <-> B+2C, but how do I do part B?

Laura Gong 3H
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Re: 6th Edition 11.89

Postby Laura Gong 3H » Mon Jan 14, 2019 2:59 pm

I haven't done this question yet, but since you you know the balanced equation and the partial pressures of each species in the reaction at equilibrium, I would write out the K expression for the reaction and plug in the values of their partial pressures at equilibrium.
Kp= P(B)*P(C)^2/P(A)^2

Hai-Lin Yeh 1J
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Re: 6th Edition 11.89

Postby Hai-Lin Yeh 1J » Mon Jan 14, 2019 3:29 pm

I did do that, but the answer in the answer key is: (5/100)(10/100)^2/(18/100)^2. Can someone explain why this is?

Kate_Santoso_4F
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Re: 6th Edition 11.89

Postby Kate_Santoso_4F » Mon Jan 14, 2019 10:34 pm

Part b asks you to calculate the equilibrium constant for the reaction. The formula to calculate the equilibrium constant is as follows:
K=(PB)*(PC)^2/(PA)^2
The partial pressures in the graph they give us are in kPA. To use the K formula, I believe you need to have the partial pressures in atm or bar. 1bar = 100 kPA. I believe thats why you get the equation:
(5/100)*(10/100)^2/(18/100)^2=1.54*10^-2
You just need to convert the partial pressures given in kPA to bar.


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