[jjkwest1]

A galvanic cell uses the reaction between solid tin and aqueous copper ions to produce electrical power.

Sn(s) + 2Cu²⁺(aq) Sn²⁺(aq) + 2Cu(s)

the reaction in the cell is allowed to proceed. as the reaction in the cell progresses, the cell potential will:
a. decrease as the concen. of Sn²⁺ increases
b. decrease as the concen of Sn²⁺ decreases
c. increase as the concen. of Sn²⁺ increases
d increase as the concen. of Sn²⁺ decreases

The book says the answer is a. I understand why this is correct because of Lechatelier's principle. but can't d. also be right b/c of the same principle? if you decrease the concen. of Sn²⁺ wont the reaction shift to the right which would therefore make the cell potential greater than it already is thereby increasing it?

[FreeTheBee]

Potential wise you are right, but the question regards the cell as it is running as a galvanic cell. Only answer a applies to that situation. Answer d would apply for the opposite process, which requires energy.