AeroLab Reading room

CHEM / A2 level

Electrode potentials and electrolysis

Standard electrode potentials compare reduction tendencies with a reference electrode under standard conditions. A positive calculated cell potential indicates the thermodynamically favoured direction under those conditions.

Learning objectives

The big idea

Standard electrode potentials compare reduction tendencies with a reference electrode under standard conditions. A positive calculated cell potential indicates the thermodynamically favoured direction under those conditions.

The Nernst relationship describes concentration effects. Faraday calculations connect charge with electron amount; kinetic barriers and overpotentials can affect observed electrode reactions.

Equations and relationships

Q = It; n(e⁻)=Q/F

Charge links current and time to electron amount.

Worked example

A current of 2.0 A flows for 300 s. Find charge.

Follow the solution

Q=It=2.0×300=600 coulombs.

Investigate and explain

Predict the worked result before calculating. Change one input, record the new result, and explain which assumptions still hold.

Use the evidence activity below; no exact PhET model is claimed.

Open the interactive investigation

Check your understanding

1. Which standard potential is subtracted to obtain Ecell?

  1. Cathode from anode always
  2. Add all potentials regardless of direction
  3. Anode reduction potential from cathode reduction potential
Check the answer and reasoning

Anode reduction potential from cathode reduction potential

Using tabulated reduction potentials, Ecell=Ecathode−Eanode.

2. A current of 2.0 A flows for 300 s. Find charge.

  1. 600 C
  2. 150 C
  3. 0.00667 C
Check the answer and reasoning

600 C

Q=It=2.0×300=600 coulombs.

3. Should electrode potentials be multiplied when balancing electrons?

  1. Yes
  2. No
  3. Only for two electrons
Check the answer and reasoning

No

Potential is energy per unit charge, an intensive quantity; balance charge without scaling E.