Reduction Potential Calculator

Look up and compare standard reduction potentials. Calculate cell potential from two half-reactions. Determine which species is the stronger oxidizing or reducing agent.

⚡ Electrochemistry📐 E°cell = E°red(cathode) - E°red(anode)🧪 Chemistry

E° half-reaction 1 (V)

E° half-reaction 2 (V)

Electrons transferred n

Please enter valid values.

Formula & Reference

Variable	Symbol	Formula	Units
Reduction Potential Calculator	See formula	E°cell = E°red(cathode) - E°red(anode)	V

Step-by-Step Examples

Example 1

Zinc-Copper Cell

E0(Cu^2+/Cu)=+0.340 V, E0(Zn^2+/Zn)=-0.763 V, n=2.

Cu^2+/Cu has higher E0: it is cathode (reduced)
Zn^2+/Zn is anode (oxidized)
E0cell = 0.340 - (-0.763) = +1.103 V

✓ E0cell = +1.103 V (Daniell cell voltage)

Example 2

Fe-Ag Cell

E0(Ag+/Ag)=+0.799 V, E0(Fe^2+/Fe)=-0.440 V, n=2.

Ag has higher E0: cathode
E0cell = 0.799 - (-0.440) = +1.239 V

✓ E0cell = +1.239 V

Example 3

Comparing Reducing Agents

Compare: Zn (-0.763 V), Fe (-0.440 V), Cu (+0.340 V) as reducing agents.

Better reducing agent = lower (more negative) E0
Order: Zn > Fe > Cu as reducing agents
Zn most readily loses electrons (most reactive metal)

✓ Zn is strongest reducing agent, Cu is weakest

Real-World Applications

🔧

Galvanic Corrosion

Metals with very different E0 form galvanic couple. More negative metal corrodes faster.

Battery Design

Standard reduction potentials determine theoretical cell voltages for battery design.

🧪

Metal Activity Series

Reduction potentials rank metals from most reactive (Li: -3.04 V) to least (Au: +1.50 V).

⚡

Electrolysis Design

Minimum voltage needed for electrolysis = E0cell for the reverse (non-spontaneous) reaction.

Common Mistakes to Avoid

⚠️

Higher E0 is always the cathode

In spontaneous cell: species with HIGHER E0 is reduced (cathode). Species with LOWER E0 is oxidized (anode).

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Cannot change E0 by multiplying

E0 is intensive property. Doubling a half-reaction does NOT change E0. Only n changes.

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E0 vs E

E0 is standard potential (standard conditions). E is actual potential (use Nernst equation for non-standard).

Frequently Asked Questions

What is the standard hydrogen electrode (SHE)? ▾

Reference electrode: 2H+ + 2e^- to H2, E0=0.000 V by definition. All other E0 values measured relative to SHE.

What does a large positive E0 mean? ▾

Strong tendency to be reduced. Fluorine (E0=+2.87 V) is the strongest oxidizing agent. Gold (E0=+1.50 V) is nearly inert.

What does a negative E0 mean? ▾

Tendency to be oxidized rather than reduced. Lithium (E0=-3.04 V) is the strongest reducing agent (most reactive metal).

Can E0 values be added directly? ▾

No. E0 values cannot be directly added (they are potentials, not energies). But when combining half-reactions: multiply by n first (dG0 = -nFE0 adds), then find E0 of combined reaction.

What is the EMF series? ▾

The electrochemical series: metals ranked by E0. Metals above hydrogen reduce H+ (react with acid). Below cannot.

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Formula Explorer connections

Interpretation: This formula links electron transfer, charge, potential, current or ionic transport in an electrochemical system. Assumption: Balance electron count and half-reactions, preserve sign conventions, and use consistent concentration, temperature and electrical units. Real cells include losses and overpotential.

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