# How can I use the Nernst equation to calculate the free energy change for oxidation reduction reactions?

##### 1 Answer

There are five steps for calculating the free energy change for an oxidation-reduction reaction. You use the Nernst equation at Step 4.

**EXAMPLE**

Calculate the free energy change for the following electrochemical cell at 25.0 °C.

Zn(s) | Zn²⁺ (1.50 mol/L) || Cu²⁺ (0.250 mol/L) | Cu(s)

**Solution**

**Step 1.** Calculate the standard cell potential,

Zn → Zn²⁺ + 2 e⁻;

Cu²⁺ + 2 e⁻ → Cu;

Zn + Cu²⁺ → Zn²⁺ + Cu;

**Step 2.** Determine the number of moles of electrons

**Step 3.** Calculate the reaction quotient,

**Step 4.** Use the Nernst equation to calculate the nonstandard cell potential,

1.101 V – 0.0230 V = 1.078 V

**Step 5.** Calculate the free energy.