Textbook Problem 5.61 Part F

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Samantha Pedersen 2K
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Textbook Problem 5.61 Part F

Postby Samantha Pedersen 2K » Mon Jan 04, 2021 5:38 pm

Problem 5.61 from the textbook says, "The overall photosynthesis reaction is 6CO2 (g) + 6H2O (l) ---> C6H12O6 (aq) + 6O2 (g), and
= +2802 kJ. Suppose that the reaction is at equilibrium. State the effect that each of the following changes will have on the equilibrium composition: tends to shift toward the formation of reactants, tends to shift toward the formation of products, or has no effect." Part F specifically asks for the effect of adding water.

The solutions manual says, "Because water is a liquid, it is by definition present at unit concentration, so changing the amount of water will not affect the reaction." I know that we don't consider liquids when calculating the equilibrium constant, but do we also not consider liquids when applying Le Chatelier's principle in a problem like this? Thank you!

Yasmina Zaarour 1G
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Re: Textbook Problem 5.61 Part F

Postby Yasmina Zaarour 1G » Mon Jan 04, 2021 6:02 pm

You are correct; we do not consider liquids when applying Le Chatelier's principle. From a mathematical perspective, if you write the K expression for this chemical equation, water does not appear in the expression, so changing its amount would not affect the ratio. The other reagents would not need to change their concentrations through shifting the reaction in order to reach equilibrium again.

Edison Tham 3D
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Re: Textbook Problem 5.61 Part F

Postby Edison Tham 3D » Mon Jan 04, 2021 6:16 pm

Hi!

I agree with Yasmina, I would also like to add that water is already in excess in these reactions (as very little water will be used up in the equilibrium reaction) and thus adding water would not affect the reaction at all.

John Calonia 1D
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Re: Textbook Problem 5.61 Part F

Postby John Calonia 1D » Tue Jan 05, 2021 4:16 pm

Pure solids and liquids are not taken into consideration in problems dealing with equilibrium. Aqueous solutions are taken into consideration only by concentration since it is not in a gaseous state.


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