What is electromotive force in Chemistry class 12th

 

In chemistry, electromotive force (EMF) refers to the voltage generated by a chemical cell (like a galvanic or voltaic cell) due to redox (reduction-oxidation) reactions happening at the electrodes.

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🔹 Definition (Chemistry Context):

EMF is the potential difference between two electrodes of an electrochemical cell when no current is flowing.

It measures the tendency of electrons to flow from the anode (where oxidation occurs) to the cathode (where reduction occurs).

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🔹 Symbol:

🔹 Unit:

Volt (V)

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🔹 Formula:

\mathcal{E}_{\text{cell}} = E^\circ_{\text{cathode}} - E^\circ_{\text{anode}}

Where:

• = standard electrode potentials (in volts)
• Measured under standard conditions:
  • 1 M concentration
  • 25°C (298 K)
  • 1 atm pressure

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🔹 Example (Daniel Cell):

Zn | Zn²⁺ (1 M) || Cu²⁺ (1 M) | Cu

• Anode (oxidation): Zn → Zn²⁺ + 2e⁻
• Cathode (reduction): Cu²⁺ + 2e⁻ → Cu

Standard electrode potentials:

\mathcal{E}_{\text{cell}} = 0.34 - (-0.76) = 1.10\text{ V}

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🔹 Importance in Chemistry:

• Predicts spontaneity of redox reactions
  • If , reaction is spontaneous
• Basis for electrochemical series
• Used in batteries, fuel cells, and corrosion studies

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