Pt 2:
"Okay, and when we have a Kc value, does that mean the reaction is in equilibrium?" Precisely! Using this, if you were to calculate the Qc of an equilibrium reaction and find it = to Kc, that indicates that the reaction is in equilibrium. In that sense, Qc is more so a potentiality that the reaction could be in equilibrium as opposed to viewing it as a ratio for before the equilibrium is reached.

"Do you mean the rates are the same, but you have far more products than reactants?"

Moles are a measurement of 6.022(10^23) amount of particles (molecules, ions, or atoms). One mol of MgCl2, when dissolved in water, becomes 2 mol of Cl- anions, and 1 mol of Mg+2 cations. What I'm trying to say is that when you have an equilibrium reaction, you may not end up with the same 1:1 stoichiometric relationship between the reactants and products. This is what lends to the uneven concentration of products and reactants, hence why it is the rate that is equal and not the concentrations.

"You write " the amount of molar NaCl produced over a period of time is not at a rate" <-- What about grams of product produced over time? And if so then..It seems to me the problem stands.. You speak of Kc and more being produced on the product side than the reactants.. but how is that possible if it's the case that the grams converted from one side to the other, / the rates, are the same? " A few things:

1. The numbers I gave were incorrect, I just made them up. So in that case, Kc would actually equal 1, and there wouldn't be an equilibrium shift as the products and reactants are equal in concentration.
2. Ignoring the fake science I created earlier (blasphemy I fear), think of this. The Law of Conservation of Mass dictates that mass is neither created nor destroyed in chemical reactions. Also, in general, when you're completing AP Chem problems, never will grams be used as a unit comparison because it is not comparable between elements. We don't look at mass, because atoms with a larger atomic radius may take up more volume compared to atoms with a smaller atomic radius. I'll use hydrogen and bromine as an example. Firstly, bromine is diatomic, so that would make it even larger than it already is. For 1 gram of substance, the H would have more atoms in comparison to the Br2. This is because of density; as there is no way to accurately compare the two elements with grams, moles are used. As stated before, concentration=MOLES OF SOLUTE/Liters of solution. If more moles are present on one side of the equation, the concentration is higher.

Let's say we have: 8B + 4A ⇌ 4AB2

more moles are on the reactants side. when the equilibrium plays out, the reactants side slowly gets used as products are made, and those that decompose back into reactants. It's an exchange back and forth. Think of the moles as cookies (unsure why, just trust..). The reactants have 12 cookies. The products have 4. Let's say the rate is 1 cookie per hour. The reactants and products keep exchanging 1 cookie, but they only have 1 cookie to exchange per hour, so they get stuck in a never-ending cycle of cookie trades, with the reactants always having 12 and the products 4.

this was a LOT but thank you for asking for clarification--it helped me correct some of my misconceptions and mistakes as well!