Galvanic Cells

This section explores galvanic cells, their variations, functions, and importance in electrochemistry. These cells utilise spontaneous redox reactions to generate electrical energy, which is pivotal for applications such as batteries.

Definition and Function

• Galvanic Cell: An electrochemical device that employs a spontaneous redox reaction to produce electrical power.

• Purpose: Transforms chemical energy into electrical energy.

  • Applied in practical devices such as batteries and other electronics.
  • Provides power to everyday items such as remote controls and torches.

Components of a Galvanic Cell

• Anode:

  • Serves as the site of oxidation.
  • Electrons are liberated and directed towards the cathode.

• Cathode:

  • Functions as the site of reduction.
  • Electrons are accepted at this location.

• Salt Bridge:

  • Preserves electrical neutrality in the system.
  • Prevents charge buildup, facilitating uninterrupted operation.

• Electrolytes:

  • Allow ion movement between electrodes.
  • Support ion flow effectively.

Working Principle

• Electron Flow:

  • Electrons travel from anode to cathode, generating current due to the potential difference.

• Ion Migration:

  • Ions transfer through the solution and the salt bridge.
  • Ensures stability by promoting uniform ion movement.

• Redox Reactions:

  • Oxidation: Defined by the loss of electrons.
  • Reduction: Characterised by the gain of electrons.

Zinc-Copper Reaction

Setup & Importance: The oxidation of zinc is akin to lighting a match, leaving electrons as residue. In contrast, copper's reduction is comparable to a sponge, absorbing these electrons to sustain continuous flow, thus generating electricity for practical uses.

• Anode Reaction:

  $\text{Zn(s)} \rightarrow \text{Zn}^{2+}(\text{aq}) + 2\text{e}^-$

• Cathode Reaction:

  $\text{Cu}^{2+}(\text{aq}) + 2\text{e}^- \rightarrow \text{Cu(s)}$

Historical Significance

• Development:

  • Pioneers such as Luigi Galvani and Alessandro Volta made significant contributions.
  • Their early experiments formed the basis of galvanic cell theory.

• Daniell Cell:

  • The first reliable galvanic cell, marking advancement in electrochemical engineering.

Visual Component

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Concentration Cells

• Definition: Concentration Cell: A form of galvanic cell using the same components at differing concentrations.
• Function: Electrical current stems from concentration gradients, akin to water levels balancing between two tanks.

Construction and Function

• Setup:
  • Comprise identical electrodes immersed in solutions of varying concentrations.
  • Segregated by a semipermeable membrane.

Nernst Equation

• Equation:

  $E = E^0 - \frac{RT}{nF} \ln\left(\frac{C_{\text{anode}}}{C_{\text{cathode}}}\right)$

• Example Calculation:

  • For a concentration cell with nickel electrodes in 0.1 M and 1 M solutions:
  • Using the Nernst equation where $R = 8.314 \text{ J/(mol·K)}$, $T = 298 \text{ K}$, $n = 2$, and $F = 96485 \text{ C/mol}$
  • $E = 0 - \frac{8.314 \times 298}{2 \times 96485} \ln\left(\frac{0.1}{1}\right)$
  • $E = 0 + 0.0592 \times 2.303 \approx 0.059 \text{ V}$

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Fuel Cells

• Definition: Fuel Cells transform chemical energy directly to electrical energy with a continuous provision of reactants.
• Eco-Friendly: Lowers carbon emissions due to negligible pollutants.

Chemical Reactions

• Anode: $2\text{H}_2 (g) + 4\text{OH}^- (aq) \rightarrow 4\text{H}_2\text{O} (l) + 4\text{e}^-$
• Cathode: $\text{O}_2 (g) + 2\text{H}_2\text{O} (l) + 4\text{e}^- \rightarrow 4\text{OH}^- (aq)$

Applications

• Automotive: Hydrogen fuel cell vehicles offer a sustainable transport solution.
• Power Generation: Provide a reliable and portable power source.

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Dry Cells

• Definition: Dry Cells: Electrochemical cells lacking free-flowing liquid electrolytes.

Chemical Reactions

• Anode (Oxidation):

  $\text{Zn(s)} \rightarrow \text{Zn}^{2+}\text{(aq)} + 2\text{e}^-$

• Cathode (Reduction):

  $2\text{MnO}_2 + 2\text{NH}_4^+ + 2\text{e}^- \rightarrow \text{Mn}_2\text{O}_3 + 2\text{NH}_3 + \text{H}_2\text{O}$

• Use: Suited for portable devices like remote controls and torches.

Comparison

Feature	Zinc-Carbon	Alkaline
Cost	Lower	Higher
Energy Density	Limited	Greater

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Reversibility in Batteries

• Definition: Reversibility: In rechargeables, reversing chemical reactions restores initial reactants.

Lead-Acid Battery

• Reactions:
  • Anode: Transformation from lead sulphate to lead.
  • Cathode: Lead oxide reforms from lead sulphate.

Lithium-Ion Battery

• Process:
  • Charging: Lithium ions accumulate energy.
  • Discharging: Ions release stored energy.

Environmental and Economic Considerations

• Environmental:

  • Reduction in waste when using rechargeables instead of disposables.

• Economic:

  • Although initially costlier, rechargeables offer long-term savings.