Chemistry

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Electromotive Force Calculator.

Calculate standard cell EMF from cathode and anode reduction potentials.

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Cell EMF: 1.1 V

Cell EMF

1.100000V

Educational chemistry arithmetic only. Keep units consistent and verify assumptions against your laboratory or course specification.

Use Cases

Predict cell voltage for a galvanic cell

Quickly determine the standard EMF of a voltaic cell by entering the standard reduction potentials of the cathode and anode half-reactions.

Example: For a Zn-Cu cell, enter cathode (Cu) = 0.34 V and anode (Zn) = -0.76 V to get EMF = 1.10 V.

Compare electrode combinations

Evaluate different electrode pairs to see which gives a higher cell potential, useful for designing batteries or electrolytic cells.

Example: Compare Cu/Zn (1.10 V) vs. Ag/Zn (1.56 V) by entering respective potentials.

Frequently Asked Questions

What is the formula used by this calculator?
The calculator uses EMF = cathode reduction potential - anode reduction potential. This gives the standard cell potential (E°cell) in volts.
What do cathode and anode reduction potentials mean?
Cathode reduction potential is the standard reduction potential of the reduction half-reaction at the cathode. Anode reduction potential is the standard reduction potential of the reduction half-reaction at the anode. The difference determines the cell's driving force.
Can I use this calculator for non-standard conditions?
No, this calculator assumes standard conditions (1 M concentrations, 1 atm pressure, 25°C). For non-standard conditions, you would need the Nernst equation.

Tips & Common Mistakes

Tips

  • Ensure you enter the reduction potentials with the correct sign (positive or negative) as given in standard reduction potential tables.
  • The cathode is the electrode where reduction occurs; it has the higher (more positive) reduction potential. The anode is where oxidation occurs.
  • Double-check that both potentials are for the same conditions (standard) and that you are using the reduction potentials, not oxidation potentials.
  • If you get a negative EMF, the reaction is non-spontaneous as written; swap the electrodes to get a positive value.

Common Mistakes to Avoid

  • Using oxidation potentials instead of reduction potentials. Always use reduction potentials for both electrodes.
  • Swapping the cathode and anode potentials, which would give a negative EMF and misrepresent the cell's polarity.
  • Forgetting to include the sign of the potentials. A common error is entering -0.76 V as 0.76 V for zinc, leading to an incorrect EMF.

Last updated: August 13, 2026