The corrosion of iron can be thought of as an electrochemical cell reaction. Calculate the voltage difference between two points of corroding iron differing only in their partial pressures of oxygen: 0.20 atm of oxygen at one point and 0.0010 atm of oxygen at the other. The reaction is: H2O + Fe (s) + 1/2 O2 (g) --> Fe(OH)2 (s)

Ecell = Eocell - (0.0592/n)*log (more dilute soln/more concd soln).

Eocell = 0 since the two electrodes are the same; i.e, this is a concentration cell.
I would plug in 0.001 for more dilute solution and 0.20 for the more concentrated solution and calculate E. I believe n=2.
Check my thinking.

To calculate the voltage difference between two points of corroding iron with different partial pressures of oxygen, you need to use the Nernst equation. The Nernst equation relates the concentration (or in this case, the partial pressure) of the reactants and products to the cell voltage.

The Nernst equation is given by:

E = E° - (RT/nF) * ln(Q)

Where:
E = cell voltage
E° = standard cell voltage
R = gas constant (8.314 J/(mol·K))
T = temperature (in Kelvin)
n = number of electrons transferred in the reaction
F = Faraday's constant (96,485 C/mol)
ln = natural logarithm
Q = reaction quotient (products over reactants)

In this case, the reaction is:

H2O + Fe (s) + 1/2 O2 (g) → Fe(OH)2 (s)

First, we need to determine the values for E° and n (the number of electrons transferred).

The standard cell potential can be found from standard reduction potentials. The standard reduction potential for the Fe(OH)2(s) → Fe2+(aq) + 2OH-(aq) half-reaction is approximately -0.88 V.

Since there is no information given about the partial pressure of hydrogen ions (H+), we can assume that it remains constant, meaning the reaction quotient Q simplifies to just the ratio of O2 pressures.

Now, we can plug in the values into the Nernst equation:

E = -0.88 V - (8.314 J/(mol·K) * T / (2 * 96,485 C/mol)) * ln(0.0010 atm / 0.20 atm)

Note: Remember to always convert temperature to Kelvin when using the Nernst equation.

The temperature is not provided, so you'll need to substitute with the desired temperature. Once you have the temperature, you can calculate the voltage difference between the two points of corroding iron.