E cell = E 0cell - RT/2F ln(P H2O / P H2 * P O2 1/2 ) Suppose you have a hydroge

Question

Ecell = E0cell - RT/2F ln(PH2O/ PH2 * PO21/2 )

Suppose you have a hydrogen-oxygen fuel cell with the overall reaction:

H2 (g) + ½ O2 (g) -> H2O (g)

The corresponding Nernst equation is given above, in which PH2O is the gas pressure of water vapor, PH2 the hydrogen gas pressure, and PO2 that of oxygen. Given the above, which of the follow statement(s) are TRUE. No knowledge of fuel cells is required – just a fundamental ability to read and interpret a mathematical expression.

(To receive credit you must select all the TRUE statements and NOT select those that are false.)

Question 3 options:

As the fuel cell runs and water vapor PH2O accumulates, the cell potential Ecell should decrease.

Temperature T has no effect on the cell potential Ecell.

If the pressure of oxygen gas PO2 is increased the cell potential Ecell will increase.

Tripling the hydrogen pressure PH2 will reduce the cell potential Ecell by 1/3.

Explanation / Answer

As the fuel cell runs and water vapor PH2O accumulates, the cell potential Ecell should decrease. TRUE

Temperature T has no effect on the cell potential Ecell. FALSE

If the pressure of oxygen gas PO2 is increased the cell potential Ecell will increase. TRUE

Tripling the hydrogen pressure PH2 will reduce the cell potential Ecell by 1/3. FALSE

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