What factors affect electrochemical cells?

1 Answer
Feb 11, 2014

The Gibbs free energy change determines the voltage of an electrochemical cell. This in turn depends on factors such as concentration, gas pressure, and temperature.

Explanation:

Gibbs Free Energy

The Gibbs free energy measures how far a system is from equilibrium.

It therefore determines the voltage (driving force) of an electrochemical cell.

ΔG = -nFEΔG=nFE or E = -(ΔG)/(nF)E=ΔGnF

where nn is the number of moles of electrons transferred and FF is the Faraday Constant.

Concentration and Gas Pressure

ΔG = ΔG° - RTlnQ, where Q is the reaction quotient.

For an equilibrium reaction such as "A" ⇌ "B + C",

Q =(["B"]["C"])/(["A"]) or Q = (P_"B" P_"C")/P_"A" if the substances are gases.

E depends on ΔG, ΔG depends on Q, and Q depends on concentration and pressure.

Therefore both concentration and gas pressure affect the voltage of the cell.

Temperature

According to the Nernst Equation,

E = E° - ((RT)/(nF))lnQ

The temperature term in this equation shows that temperature also affects the cell voltage.