7.2 Electrochemistry and Galvanic Cells

Electrochemical cells are the unsung heroes of modern technology. From powering our devices to detecting diseases, these tiny powerhouses convert chemical energy into electrical energy, revolutionizing how we live and work.

Understanding the components and principles of electrochemical cells is crucial. We'll explore how anodes, cathodes, and salt bridges work together to create electricity, and how cell potentials are calculated and applied in real-world scenarios like biosensors and fuel cells.

Electrochemical Cells and Their Applications

Components of galvanic cells

• Anode oxidizes, acts as negative electrode, loses electrons (zinc electrode in Daniell cell)
• Cathode reduces, acts as positive electrode, gains electrons (copper electrode in Daniell cell)
• Salt bridge maintains electrical neutrality, allows ion flow between half-cells (KCl solution)
• Voltmeter measures cell potential difference between electrodes
• Half-cells separate compartments for each electrode, contain electrolyte solutions (CuSO₄, ZnSO₄)

Calculation of standard cell potential

• Standard reduction potentials tabulated for half-reactions, measured relative to standard hydrogen electrode (SHE)
• Cell potential calculation uses formula $E^°_{cell} = E^°_{cathode} - E^°_{anode}$, always positive for spontaneous reactions
• Nernst equation $E = E^° - \frac{RT}{nF}\ln Q$ relates cell potential to non-standard conditions
• Concentration effects impact cell potential, higher reactant concentration or lower product concentration increases potential

Gibbs free energy vs cell potential

• Gibbs free energy and cell potential related by $\Delta G = -nFE$, n represents electrons transferred, F is Faraday constant
• Spontaneous reactions have negative $\Delta G$ and positive $E_{cell}$
• Standard conditions use $\Delta G^° = -nFE^°$ to calculate equilibrium constants

Applications in biosensors and fuel cells

• Biosensors utilize enzyme-based electrochemical reactions (glucose meters), detect specific DNA sequences (genetic testing)
• Fuel cells convert chemical energy to electrical energy (hydrogen fuel cells in vehicles), utilize bacteria for electricity generation (microbial fuel cells for wastewater treatment)
• Implantable medical devices employ long-lasting lithium-iodine batteries (pacemakers), rechargeable batteries for continuous operation (cochlear implants)