Electrochemistry: Galvanic and Electrolytic Cells

• Electrochemistry is the study of chemical processes causing electron movement
• Electron movement generates electricity for powering devices or drives non-spontaneous chemical reactions when electricity is applied.
• Electrochemical reactions are redox reactions involving electron transfer.
• Oxidation is the loss of electrons while reduction is the gain of electrons; both always occur together
• The substance oxidized is the reducing agent; the substance reduced is the oxidizing agent.
• Electrochemical cells convert chemical energy to electrical energy and vice versa
• Galvanic cells (voltaic cells) convert chemical energy into electrical energy.
• Electrolytic cells convert electrical energy into chemical energy.
• A galvanic cell contains two half-cells, each with an electrode in electrolyte solution
• The half-cells connect via a salt bridge, allowing ion flow to maintain charge balance.
• Oxidation occurs at the anode
• Reduction happens at the cathode
• Electrons flow from anode to cathode via an external circuit
• Electron flow creates electric current.
• Cell potential (Ecell) is the electrical potential difference between cathode and anode.
• Cell potential measures the electrochemical reaction's driving force and is also known as electromotive force (EMF)
• Standard cell potential (E°cell) is the cell potential when reactants and products are in standard states (1 M for solutions, 1 atm for gases, pure solids/liquids).
• Standard reduction potential (E°red) refers to a half-cell's potential under standard conditions, relative to the standard hydrogen electrode (SHE)
• The SHE has a standard reduction potential of 0 V
• Cell potential is calculated as: E°cell = E°cathode - E°anode.
• A positive cell potential means the reaction is spontaneous under standard conditions; a negative potential means it's non-spontaneous
• The Nernst equation relates cell potential to standard cell potential and the reaction quotient (Q): Ecell = E°cell - (RT/nF) ln Q
• R is the ideal gas constant (8.314 J/mol·K).
• T is temperature in Kelvin.
• n is the number of moles of electrons transferred in the balanced redox reaction.
• F is the Faraday constant (96,485 C/mol).
• The reaction quotient (Q) measures relative amounts of reactants and products at a given time
• Electrolytic cells use electrical energy to drive non-spontaneous reactions.
• Electrolysis uses electrical energy to decompose a compound.
• Electrolysis has uses in industrial processes such as producing aluminum, chlorine, and sodium hydroxide
• In an electrolytic cell, the anode is positive and the cathode is negative
• Electrons are forced to flow from anode to cathode using an external power source
• The amount of product formed during electrolysis relates to the amount of charge passed through the cell
• Faraday's law: The amount of substance produced or consumed at an electrode is directly proportional to the amount of electricity passed through the cell
• Charge (Q) passed through the cell is calculated as Q = It
• I is current in amperes; t is time in seconds
• The amount of substance (in moles) produced or consumed is calculated as moles = Q/nF
• n is the number of moles of electrons transferred per mole of substance.
• Corrosion is the oxidation of a metal and is an electrochemical process
• Rusting of iron is a common example of corrosion
• Corrosion prevention includes coating metal with a protective layer or using a sacrificial anode
• Sacrificial anode: A metal that is more easily oxidized than the metal it protects
• The sacrificial anode corrodes instead of the metal it is protecting
• Batteries are galvanic cells that store and provide electrical energy
• Different battery types: dry cells, lead-acid batteries, and lithium-ion batteries
• Fuel cells convert chemical energy of a fuel and oxidant into electrical energy
• Fuel cells are similar to batteries but do not need recharging
• Fuel cells operate continuously with fuel and oxidant supply
• The hydrogen fuel cell is the most common, using hydrogen as fuel and oxygen as oxidant.

Electrochemistry studies chemical processes causing electron movement. Electrochemical reactions are redox reactions involving electron transfer, where oxidation is loss and reduction is gain. Galvanic cells convert chemical energy to electrical energy, while electrolytic cells convert electrical energy to chemical energy.