Electrochemistry
Class 12 · Chemistry
4 ideas in Class 12 Chemistry, explained in plain words, with games and quizzes to practise.
Galvanic Cells and Electrode Potential
Part of: Cells and Nernst Equation
Galvanic cells split oxidation and reduction into two beakers joined by a salt bridge, with electrons running anode to cathode. Potentials are ranked against hydrogen's zero, and cell emf is cathode minus anode, positive for spontaneous Daniell-type cells.
Why it matters. Batteries, plating and corrosion all follow cell emf signs. Swapping anode with cathode flips every prediction.
Formulas
- Cell emf: Ecell = Ecathode - Eanode
- SHE potential fixed at 0 V
- Positive Ecell means spontaneous reaction
Key words
- Anode
- : Electrode where oxidation releases electrons, negative in a cell.
- Cathode
- : Electrode where reduction consumes electrons, positive in a cell.
- Salt bridge
- : Ion path completing the circuit and balancing charge.
- Standard hydrogen electrode
- : Zero-volt reference with hydrogen at unit conditions.
Try it in two minutes
- Mark oxidation at anode, reduction at cathode.
- Read both standard potentials.
- Subtract anode from cathode for emf.
Try at home. Predict whether iron nails rust faster in salt water and why.
Nernst Equation and Gibbs Energy
Part of: Cells and Nernst Equation
Cell emf slides from standard by 0.0591 over n times log of the reaction quotient, matching E with a hydrogen electrode at pH shifts. Gibbs energy is minus nF times emf, and equilibrium constant follows from zero emf, growing huge for spontaneous cells.
Why it matters. Real cells never sit at 1 M, and pH meters read Nernst slopes. Dropping the log term or the electron count wrecks every number.
Formulas
- Nernst: E = E0 - (0.0591/n) log Q
- Gibbs: dG0 = -n F E0
- Equilibrium: Ecell = 0 at K
Key words
- Nernst equation
- : Emf under actual concentrations from standard emf.
- Reaction quotient
- : Product over reactant concentration ratio at any moment.
- Equilibrium constant
- : Quotient value where cell emf reaches zero.
Try it in two minutes
- Write the quotient with product over reactant powers.
- Subtract 0.0591 over n times its log.
- Multiply emf by minus nF for Gibbs energy.
Try at home. Predict how diluting copper ions shifts a Daniell cell.
Conductance and Kohlrausch Law
Part of: Conductance and Batteries
Conductivity counts ions per volume and falls on dilution, while molar conductivity per mole rises, steeply for weak electrolytes that dissociate more. Kohlrausch adds independent ion shares at infinite dilution, giving weak-electrolyte limits and dissociation fractions.
Why it matters. Water testing, plating baths and weak-acid strengths all use these trends. Confusing the two conductivities reverses every dilution answer.
Formulas
- Molar: Lm = k x 1000 / M
- Weak electrolytes rise steeply with dilution
- Dissociation: alpha = Lm / L0m
Key words
- Conductivity
- : Conductance of one centimetre cube of solution.
- Molar conductivity
- : Conductivity per mole of dissolved electrolyte.
- Kohlrausch law
- : Ions migrate independently, adding fixed shares at infinite dilution.
- Degree of dissociation
- : Fraction split into ions, equal to molar ratio at dilutions.
Try it in two minutes
- Multiply cell constant by conductance for conductivity.
- Scale by 1000 over molarity for molar conductivity.
- Add ion shares for the infinite-dilution limit.
Try at home. Compare conductivity of vinegar and salt water at equal molarity.
Batteries, Fuel Cells and Corrosion
Part of: Conductance and Batteries
Dry cells give 1.5 V once, mercury cells hold steady for devices, and lead storage banks six 2 V cells rechargeably. Hydrogen-oxygen fuel cells make power plus water without pollution. Rusting is an iron-air-water cell, blocked by paint, oiling or zinc sacrifice.
Why it matters. Cars, phones, space power and bridges all depend on these. Expecting primary cells to recharge, or rust without moisture, breaks practical answers.
Formulas
- Dry cell about 1.5 V; lead cell about 2 V each
- Car battery: six lead cells near 12 V
- Fuel cell: hydrogen plus oxygen gives water plus power
Key words
- Primary cell
- : One-use cell like the dry cell.
- Secondary cell
- : Rechargeable cell like lead storage.
- Fuel cell
- : Cell fed continuously with fuel and oxygen.
- Galvanisation
- : Zinc coating that sacrifices itself to protect iron.
Try it in two minutes
- Sort cells into primary, secondary and fuel types.
- Multiply lead cells by 2 V for battery voltage.
- Cover iron or attach zinc to stop rust.
Try at home. List cells at home by rechargeable or not.
What your child will practise
- Batteries, Fuel Cells and Corrosion: Space Quick Fire (Quick Fire)
- Conductance and Kohlrausch Law: Ocean Puzzle (Clue Puzzle)
- Conductance and Kohlrausch Law: Ocean Quick Fire (Quick Fire)
- Galvanic Cells and Electrode Potential: Jungle Quick Fire (Quick Fire)
- Nernst Equation and Gibbs Energy: Candy Puzzle (Clue Puzzle)
- Quiz: Batteries, Fuel Cells and Corrosion (8 questions)
- Quiz: Conductance and Kohlrausch Law (8 questions)
- Quiz: Galvanic Cells and Electrode Potential (8 questions)
- Quiz: Nernst Equation and Gibbs Energy (8 questions)