<p>Well, you’ve lost me there with the mole stuff.
You don’t chose what you want to decrease the concentration of, the concentration of products and reactants increases/decreases according to the factor given.
The conc. of products will <em>not</em> decrease with the given factor.
Think about it. what is reacting together - A(g) and B(g) - you make the volume smaller - they are bumping into eachother more frequently and colliding more and more - producing more C(g) - concentration of C increases.
Volume decrease, pressure increase - basically the same factor.
Don’t really understand how the mole stuff works out but to get back to the original topic - pressure does affect concentrations in equilibrium reactions involving gases.
Also, editing posts gets confusing.</p>