stonecold's chem questions :)

[lisafaustina]

What if you take the cathode reaction of an alkaline cell for instance?
the equation is 2MnO2 +H2O ---> Mn2O3 +2OH-
shouldn't you be adding water to the right hand side of he equation to start with, then add the H+s then the OH-s?

[cypriottiger]

What if you take the cathode reaction of an alkaline cell for instance?
the equation is 2MnO2 +H2O ---> Mn2O3 +2OH-
shouldn't you be adding water to the right hand side of he equation to start with, then add the H+s then the OH-s?

errr....explain please? because from here it sounds like your saying add more H2O product. from my knowledge adding a volume moves the reaction to the more particle side, but as they are even, there would be no change in equilibrium constant

[Mao]

What if you take the cathode reaction of an alkaline cell for instance?
the equation is 2MnO2 +H2O ---> Mn2O3 +2OH-
shouldn't you be adding water to the right hand side of he equation to start with, then add the H+s then the OH-s?

Yes.

[lisafaustina]

What if you take the cathode reaction of an alkaline cell for instance?
the equation is 2MnO2 +H2O ---> Mn2O3 +2OH-
shouldn't you be adding water to the right hand side of he equation to start with, then add the H+s then the OH-s?

Yes.

THANK YOU MAo

[stonecold]

These are two questions from NEAP 09 which I didn't really know how to do.  I've got no idea how to approach the equation for the first question.  I checked the answers, but I've got no idea how to arrive at what they did systematically. For the second question, it says a reaction will occur due to the concentration differences or something.  Confusing!!!

I really suck at the whole galvanic cell thing.  I rushed through it all.  I get the basics, but once it deviates from the ECS and I have to work from given equations, I really have no idea what I am doing...

[iffets12345]

Is the answer for the second question no flow?

[fady_22]

Is the answer for the second question no flow?

The conditions aren't standard. There could be a current (it is likely that there would be, seeing as there is a large difference in concentration between the two cells).

[Whatlol]

Is the answer for the second question no flow?

no there is a flow due to the uneven concentrations

[stonecold]

Is the answer for the second question no flow?

Nope.  I nearly fell off my chair when I was marking it.

This is the answer.

[stonecold]

Is the answer for the second question no flow?

no there is a flow due to the uneven concentrations

Where do you learn this stuff?  I know I probably forgot it, but I don't remember seeing it in the textbook.  All it said was that species would behave differently if the conditions weren't 1M, 1 atm, 25 C.

[iffets12345]

bring on the fail for unit 4 CHYEAHH

[Whatlol]

Is the answer for the second question no flow?

no there is a flow due to the uneven concentrations

Where do you learn this stuff?  I know I probably forgot it, but I don't remember seeing it in the textbook.  All it said was that species would behave differently if the conditions weren't 1M, 1 atm, 25 C.

My teacher told me but i dont really understand why to be honest, all i was told is something to do with the inbalance of concentrations can cause a reaction to occur. Then i wondered off possibly more confused than before i didnt know.

Hopefully Mao or someone can provide the reasoning.
sorry

[kakar0t]

It's because at 1M concentration the two cells would have an equal potential difference and when you link up two 1M half-cells of the same electrode and shit together it will cancel out to give you 0 potential difference so charge (and hence current) will not flow between the two.

However, when you link a 1M half-cell up with a (lets say) 4M half-cell, the 4M does not have a standard potential difference (e naught) value given by the electrochemical series, it is quite different due to not being in Standard Lab Conditions (SLC), which is what the electrochemical series in our data books are determined from.

So since it is a non-standard cell, we can deduce that the 4M half-cell will have a different potential compared to the 1M half-cell, and when we link them up via a wire, the potential differences will add to give a non-zero difference across the whole cell and thus current should flow.

[fady_22]

Is the answer for the second question no flow?

Nope.  I nearly fell off my chair when I was marking it.

This is the answer.

Don't forget-- equilibrium rules still apply here.
If the concentration increases, this means that the reaction is driven forward, making it a stronger oxidant (increasing the cell potential). Thus there is a difference in cell potentials, causing a current to flow.

[stonecold]

What are people getting for part c?