# How&why does change in concentration affect cell potential

I'm a bit confused about why (in 1c) if the air pressure is lower, and there is a lower concentration of oxygen, why the cell potential decreases.

It checks out fine with the Nernst Equation, but conceptually, voltage is the driving force or energy of the current. Wouldn't there just be less electrons, not a lower voltage?

Like how the standard reduction potential isn't based on moles of reactant?

• Wondering as to why this was downvoted – Saketh Malyala Sep 24 '18 at 8:11

Think about it this way. Oxygen will diffuse into the cathode regardless if current is flowing or not. Obviously an infinite amount of oxygen can't flow into the cathode, or else all the oxygen would be sucked out of earth's atmosphere. So there has to be some distribution coefficient, D, that gives the limit of how much oxygen the cathode can absorb. The notion here is that if 100% oxygen allows an amount $$x$$ of oxygen to diffuse into the electrode, the the atmosphere with roughly 20% oxygen and 80% nitrogen would allow $$0.20x$$ amount of oxygen to diffuse into the electrode. Thus much akin to the Nernst Equation for liquids applies and the cell voltage with only 20% oxygen is lower than if the cell is in 100% oxygen.