9.9 Cell Potential and Free Energy

Calculating Cell Potential

In the previous lesson, we learned how different chemical species have different reduction potentials. Using these reduction potentials, we can calculate the overall cell potential of an electrochemical cell.

For example, let’s say we have an electrochemical cell with Zinc and Copper, whose reduction potentials are shown below.

${Cu^{2+}+2e^- \rightarrow Cu}$ ${E_{red}=0.34V}$

${Zn^{2+}+2e^- \rightarrow Zn}$ ${E_{red}=-0.76V}$

If we consider a galvanic cell, it will need to have a net positive cell voltage for it to run. Since copper has a higher reduction potential, it will be the species that actually gets reduced, meaning that zinc gets oxidized, meaning we can flip the chemical reaction to get:

${Zn \rightarrow Zn^{2+}+2e^-}$ ${E_{ox}=0.76V}$

Now to find the net cell potential, we can add the two reactions and values to get that:

${Cu^{2+}+Zn \rightarrow Zn^{2+}+Cu}$ ${E_{cell}=1.10V}$