Derivation of the Equilibrium Constant

[gsingh2011]

I'm trying to understand this: http://en.wikipedia.org/wiki/Equilibrium_constant#Derivation_from_Gibbs_Free_Energy
And there are few steps that I don't get. My first question is probably a stupid one, but where does the $$\Sigma$$v$$_{j}$$A$$_{j}$$=0 come from? What exactly is it summing up, the number of atoms? Are you assuming that the products side is negative? (Because I don't see how else you would get zero) And why does it only go up to n?

I'll ask my other questions after I get some replies because it's possible I'll figure them out after I read the replies.

 

[Borek]

where does the $$\Sigma$$v$$_{j}$$A$$_{j}$$=0 come from? What exactly is it summing up, the number of atoms? Are you assuming that the products side is negative? (Because I don't see how else you would get zero) And why does it only go up to n?

My guess is it is just a mass conservation, and yes, products are negative.

 

[gsingh2011]

My guess is it is just a mass conservation, and yes, products are negative.

Ok, but why does it only sum up to n? The first equation in the derivation shows the first product being n but then shows more products after that. If it was mass conservation, wouldn't it have to sum passed n?

 

[Borek]

Where does it sum only to n? It sums for all j.