A galvanic cell is based on the half-reactions; Cr3+ + 3e– → Cr E˚ = –0.744 V Ni2+ + 2e– → Ni E˚ = – — Electrochemistry Chemistry Question
Problem Context
A galvanic cell is based on the half-reactions;
Cr3+ + 3e– → Cr E˚ = –0.744 V
Ni2+ + 2e– → Ni E˚ = –0.236 V
Write the balanced equation for the overall cell reaction.
Model Answer
2Cr + 3Ni2+ → 2Cr3+ + 3Ni
State which electrode increases in mass as the cell operates. Explain your answer.
Model Answer
The nickel electrode increases in mass as the cell operates because Ni2+ ions in solution are reduced there (it is the cathode) and are deposited as Ni(s).
Calculate E˚cell
Model Answer
E˚cell = E˚red + E˚ox = –0.236 V + 0.744 V = 0.508 V
Determine the value of ∆G˚ for the cell reaction at 25˚C.
Model Answer
∆G˚ = –nFE = –(6 mol)(96500 J·mol–1·V–1)(0.508 V) = –294000 J = –294 kJ
Calculate the value of K for the cell reaction at 25˚C.
Model Answer
∆G˚ = –RTlnK
–294100 J = –(8.314 J·mol–1·K–1)(298 K) lnK
lnK = 118.7 and K = 3.62×10^51
or
K = 10^(nE˚ / 0.0592) = 10^(3.048 / 0.0592) = 3.1×10^51
Find the voltage of the cell at 25˚C if [Cr3+] and [Ni2+] are both changed to 0.010 M.
Model Answer
= 0.508 V – (0.0257/6) ln(100) V = 0.508 – 0.0197 V = 0.488 V