Chemistry EMF

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RebmaKopy
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#1
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#1
With the question below I don't understand why emf increases with increasing oxygen pressure.

(Questions 2aii is the question im referring to)
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Pigster
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(Original post by RebmaKopy)
With the question below I don't understand why emf increases with increasing oxygen pressure.

(Questions 2aii is the question im referring to)
What effect (if any) would increasing P have on the O2 <-> OH- equilibrium position and hence EMF?
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RebmaKopy
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(Original post by Pigster)
What effect (if any) would increasing P have on the O2 <-> OH- equilibrium position and hence EMF?
Increasing the pressure would mean equilibrium shifts to the right?


But how is there an equilibrium, as the overall effect is 2H + O2 → 2H2O
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Pigster
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(Original post by RebmaKopy)
Increasing the pressure would mean equilibrium shifts to the right?


But how is there an equilibrium, as the overall effect is 2H + O2 → 2H2O
There are two half-equations (one reduction, t'other oxidation), both of which add up to your stated overall equation.
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RebmaKopy
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(Original post by Pigster)
There are two half-equations (one reduction, t'other oxidation), both of which add up to your stated overall equation.
I don't understand, if the pressure is increasing surely it would only have an effect if the reaction is at equilibrium ?
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Pigster
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(Original post by RebmaKopy)
I don't understand, if the pressure is increasing surely it would only have an effect if the reaction is at equilibrium ?
EMF is measured when (as close as possible) no current is flowing and hence the two half cells are at equilibrium (as much as possible).

An analogy would be to ask you whether conc. of a dissolved ion affects emf?
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RebmaKopy
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(Original post by Pigster)
EMF is measured when (as close as possible) no current is flowing and hence the two half cells are at equilibrium (as much as possible).

An analogy would be to ask you whether conc. of a dissolved ion affects emf?
Oooo okay, I'll keep the analogy in mind, thanks!

So when we increase pressure the equilibrium shifts to the right to oppose the change, causing the reaction to shift against e-s being produced (as the reduction of oxygen is being favoured), hence, the emf decreases as the overall electrode potential becomes more positive.
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Pigster
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(Original post by RebmaKopy)
Oooo okay, I'll keep the analogy in mind, thanks!

So when we increase pressure the equilibrium shifts to the right to oppose the change, causing the reaction to shift against e-s being produced (as the reduction of oxygen is being favoured), hence, the emf decreases as the overall electrode potential becomes more positive.
The direction the equilibrium moves will depend on the side the gas is on. Assuming the gas is on the LHS, the equilibrium will push to the RHS.
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lhh2003
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(Original post by RebmaKopy)
With the question below I don't understand why emf increases with increasing oxygen pressure.

(Questions 2aii is the question im referring to)
Is this for the OCR A spec ?
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RebmaKopy
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(Original post by lhh2003)
Is this for the OCR A spec ?
AQA
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RebmaKopy
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(Original post by Pigster)
The direction the equilibrium moves will depend on the side the gas is on. Assuming the gas is on the LHS, the equilibrium will push to the RHS.
Thank you!
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