The amount of Ni(CN)_4^2- is found to increase with decreasing temperature. What

Question

The amount of Ni(CN)_4^2- is found to increase with decreasing temperature. What does this indicate about Delta H for the reaction? Explain your answer. Consider the following pair of half cells in an electrochemical cell. Cr^3+ + 3 e^- rightarrow Cr(s) E degree = -0.74 V Ag^+ + e^- rightarrow Ag(s) E degree = +0.80 V Which electrode would be the cathode and which would be the anode in a spontaneous (galvanic) electrochemical cell? An electrochemical cell is constructed with 1 times 10^-3 M concentrations of the respective ion (Cr^3+ or Ag^+) in each of the Cr and Ag half cells. Determine E_cell for this cell.

Explanation / Answer

Q1.

for Ni(CN4)-2

note that concentration increases as we decrease T, therefore this must be eoxthermic, because as we remove heat from the reaction, we favour even more products,  Ni(CN4)-2, to react.

Q2.

a)

cathode --> the reduction, in this case, highest potential, silver

anode --> the oxidatoin, in this case, lowest potential, chromium

b)

E° = ERed - Eox = 0.80 --0.74 = 1.54

E = E° -0.0592/n*log(Q)

E = 1.54 -0.0592/3*log((10^-3)/(10^-3)^3)

E = 1.4216 V

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