14.37a [ENDORSED]

[Sirajbir Sodhi 2K]

In this problem, we are able to determine that it is a concentration cell with the OVERALL reaction:

2H+ (aq, 1 M) + H2 (g, 1 atm) ----> 2H+ (aq, 0.075M) + H2 (g, 1 atm)

The solution manual includes the H2 gas in the expression for Q. I was wondering why it does when the partial pressures of H2 are the same.

Can there actually be a case in which the partial pressures of H2 on the reactants and products side are different in this concentration cell? Would such a situation arise from changing [H+]?

[Chem_Mod]

Based on the equation you gave the H₂ partial pressures are the same.

They are included in the reaction to help understand that hydrogen gas is involved in the reaction.

Yes the partial pressures in a concentration cell could be different.

The partial pressures can be independent of solution concentrations by changing the pressure of the gas.

Good questions. I should use some of them in exams. :-)

[Sirajbir Sodhi 2K]

Thank you!

One follow-up question, though: in this concentration cell, can the partial pressure of H2 on the products side of the equation be different from the partial pressure of H2 on the reactants side? (Both sides of the equation don't have H2 with a partial pressure of 1 bar)

[Chem_Mod]

Yes partial pressures can be different.