Plugging in #s for Q [ENDORSED]

[Tara_Shooshani_3N]

In the equation E=E - (RT)/(nF) * ln(Q), how do we know which molecules are the products and which are the reactants to plug in for Q? Is it always the cathode, or always the anode, or based off something else entirely?

Thanks

[Chem_Mod]

Reactants decrease over time, while products increase with time. Let's now parallel it to anode and cathode. The concentration of ion in solution in the anode increases over time (as part of the electrode breaks down and goes into solution) while the concentration of ion in solution for the cathode decreases over time (as the ions in solution attach onto the electrode).

Concentration of the anode increases over time, similar to that of products.
Concentration of the cathode decreases over time, similar to that of reactants.

Thus you can equate products with anode and reactants with cathode.

[Katrina_Domingo_3G]

What if both pressure and molarity are involved? Like in problem 14.37 c?

Pt (s) | Cl2 (g, 250 Torr) | HCl (aq, 1.0M) || HCl (aq, 0.85M) | H2 (g, 125 Torr) | Pt (s)

Can you please explain how we're supposed to plug in values for Q if this was the case?