# What factors affect electrochemical cells?

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 = -nFE or E = -(ΔG)/(nF)

where $n$ is the number of moles of electrons transferred and $F$ is the Faraday Constant.

Concentration and Gas Pressure

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

For an equilibrium reaction such as $\text{A" ⇌ "B + C}$,

$Q = \left(\left[\text{B"]["C"])/(["A}\right]\right)$ 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.