Electrode Kinetics: Exchange Current and Overpotential · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Why real electrodes need extra voltage

Science · Chemistry · ages 21-22
Name ______________________   Date ____________

  1. What is overpotential?

    • A bookkeeping error in the voltage meter
    • Extra voltage beyond the thermodynamic value that slow kinetics demands
    • Zero net current at equilibrium

  2. What is exchange current density?

    • Equal forward and backward currents at equilibrium with zero net change
    • Extra voltage beyond the thermodynamic value
    • Maximum current capped by diffusion

  3. Which surface needs only a tiny overpotential for hydrogen evolution?

    • Mercury
    • Both need the same large push
    • Platinum

  4. Standard potentials alone do not explain why brine electrolysis gives chlorine. What explains it?

    • The meter was misread
    • Overpotential lets a faster rival win despite a friendlier potential
    • Equilibrium was reached early

  5. You sweep voltage and the current climbs steeply, then flattens. Which region is the flat part?

    • Diffusion limited plateau where arrival caps current
    • Kinetically controlled climb near equilibrium
    • Zero traffic at equilibrium

  6. Near equilibrium the current climbs steeply with voltage in the kinetically controlled region.

    Circle one:   True   False

  7. A large exchange current means a slow crawling reaction.

    Circle one:   True   False

  8. Two oxidations are possible, but the one with the friendlier potential carries a huge overpotential on your electrode. Which product do you expect?

    • Always the one with the friendlier potential
    • Neither, since equilibrium blocks both
    • The faster rival with the smaller kinetic cost
LightMySky · lightmysky.comW1-mt__z7Y780pyo-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

Why real electrodes need extra voltage W1-mt__z7Y780pyo-s1

  1. Extra voltage beyond the thermodynamic value that slow kinetics demands · Slow electron transfer and surface steps must be paid for in volts.
  2. Equal forward and backward currents at equilibrium with zero net change · It measures the willing back and forth traffic when net current is zero.
  3. Platinum · Platinum offers a fast surface path, while mercury is hostile to the same steps.
  4. Overpotential lets a faster rival win despite a friendlier potential · Competing paths carry crushing kinetic penalties, so the faster rival wins.
  5. Diffusion limited plateau where arrival caps current · Flat means reactants cannot reach the surface faster than they arrive.
  6. True · Steep climb means kinetics sets the pace before diffusion caps it.
  7. False · Large means fast and willing, while tiny means slow.
  8. The faster rival with the smaller kinetic cost · Winner is decided by rates too, not by thermodynamics alone.
Worksheet · LightMySky