Chem Equilibrium Module 4 #15  [ENDORSED]

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Michelle Dong 1F
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Chem Equilibrium Module 4 #15

Postby Michelle Dong 1F » Mon Nov 27, 2017 10:19 am

15. The photosynthesis reaction, 6 CO2(g) + 6 H2O(l) ⇌ C6H12O6(aq) + 6 O2(g), is endothermic. What effect will the following changes have on the equilibrium composition.
a) Water is added.
b) The partial pressure of CO2 is decreased.

I thought that liquids have no effect on the equilibrium composition for a reaction, but all of the answer choices suggest that the addition of water changes something about the [C6H12O6(aq)]. Can someone explain this?

Jingyi Li 2C
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Re: Chem Equilibrium Module 4 #15  [ENDORSED]

Postby Jingyi Li 2C » Mon Nov 27, 2017 2:14 pm

The liquids have no effect on the equilibrium constant K, not the equilibrium composition. Remember the equilibrium composition is the concentration of each chemical at equilibrium. In this reaction, water is the reactant. Therefore, when water is added, the reaction will shift to the right to minimize the effect and [C6H12O6(aq)] will increase.

Chem_Mod
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Re: Chem Equilibrium Module 4 #15

Postby Chem_Mod » Mon Nov 27, 2017 2:14 pm

In this situation, liquid water is a part of the reaction. According to Le Chatelier's Principle, if more reactant is added then more CO2 will react and more product will be made. If the reaction did not include water however, then the addition of water will not affect the amount of product that is made.

JamesAntonios 1E
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Re: Chem Equilibrium Module 4 #15

Postby JamesAntonios 1E » Mon Nov 27, 2017 2:34 pm

Chem_Mod wrote:In this situation, liquid water is a part of the reaction. According to Le Chatelier's Principle, if more reactant is added then more CO2 will react and more product will be made. If the reaction did not include water however, then the addition of water will not affect the amount of product that is made.

If you added water, and water was not in the equation, wouldn't the concentrations of the reactants decrease thought?

Chem_Mod
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Re: Chem Equilibrium Module 4 #15

Postby Chem_Mod » Mon Nov 27, 2017 2:41 pm

Note also that adding water will decrease the concentration of the aqueous solution (ex. C6H12O6(aq) in this case), so adding water not only increase the amount of liquid water but also decrease the concentration of glucose, so the reaction will shift towards the right.

Michelle Dong 1F
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Re: Chem Equilibrium Module 4 #15

Postby Michelle Dong 1F » Mon Nov 27, 2017 4:56 pm

Thanks everyone!
I had another question: if a reactant was a solid and amount of solid was increased, would the reaction move to products side as well?

Isa Samad 1L
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Re: Chem Equilibrium Module 4 #15

Postby Isa Samad 1L » Sat Dec 09, 2017 9:57 pm

In the textbook, 11.115 is a similar question which asks what will happen to the photosynthesis reaction when water is added. However in the solutions manual, it says that the reaction is unaffected since water is a pure liquid with unit concentration and the concentration of glucose will remain dilute. So does the equilibrium shift or is it unaffected?


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