In electrochemistry, Gibbs free energy (ΔG) and cell potential (E) are directly related, because both describe the energy changes in an electrochemical reaction. Here’s a explanation:
1. Connection between ΔG and E
- A chemical reaction in an electrochemical cell can do electrical work.
- The maximum work obtainable from a cell is given by Gibbs free energy.
- The relationship is:
- Negative ΔG → spontaneous reaction → positive cell potential (E).
- Positive ΔG → non-spontaneous reaction → negative cell potential (E).
2. What it means practically
- ΔG tells us how much energy is available to do work.
- E tells us how much voltage the cell can produce.
- Larger cell potential → more negative ΔG → more energy available → reaction is more spontaneous.
3. Examples
- Galvanic cells (like a Zn-Cu battery):
- Zn loses electrons, Cu gains electrons.
- The cell has a positive potential → ΔG is negative → reaction occurs spontaneously.
- Electrolytic cells:
- Non-spontaneous reactions require external voltage.
- ΔG is positive → E is negative (needs input energy).
Summary
- ΔG and E are directly connected:
- Spontaneous reaction → ΔG < 0 → E > 0
- Non-spontaneous reaction → ΔG > 0 → E < 0
- This relationship allows chemists and engineers to calculate how much energy an electrochemical cell can produce and whether a reaction will occur on its own.