GALVANIC CELL 

1.The cell which converts chemical energy to electrical energy is called Galvanic or Voltaic cell

2.Galvanic or Voltaic cell redox reaction is

 \(\boxed{Zn_{(s)}+Cu_{(qq)}^{2+}\to Zn^{2+}_{(aq)}+Cu_{(s)}}\)

3.The example for Gavanic or Voltaic cell is Daniel cell

4.The cell notation of Daniel (Galvanic cell is 

\(\boxed{Zn_{(s)}|Zn^{+2}_{(aq)} (C_1)|| Cu^{+2}_{(aq)}(C_2)|Cu_{(s)}}\)

5.EMF of the cell is calculated by 

\(\boxed{E_{cell}=E_{right}-E_{left} (or) E_{cell}=E_{cathode}-E_{anode}}\)

A potential difference develops between the electrode and the electrolyte which is called electrode potential. 

• In a galvanic cell, the half-cell in which oxidation takes place is called the anode, and it has a negative potential.
• Reduction takes place in the cathode, which has a positive potential with respect to the solution. 
• The potential difference between the two electrodes of a galvanic cell is called the cell potential and is measured in volts. The cell potential is the difference between the electrode potentials (reduction potentials) of the cathode and anode, called the cell electromotive force (emf), calculated with - 

We arbitrarily choose the potential of one electrode (half-cell), then that of the other can be determined with respect to this. According to convention, a half-cell called the standard hydrogen electrode is assigned zero potential at all temperatures.

The electrode is dipped in an acidic solution, and pure hydrogen gas is bubbled through it. 

For a given electrode reaction:

The Nernst equation can be written as:

In relation to the equilibrium constant, 

The fundamental relation between Gibbs Energy, Cell Potential and Equilibrium Constant is given by the Thermodynamic triangle:

The flow of current in a solution is carried by ions. We quantify this with two key terms:

1. Conductivity (K): The intrinsic ability of a solution to conduct electricity. It is the conductance of a 1m³ cube of solution. (Trend: Conductivity decreases upon dilution because there are fewer charge-carrying ions per unit volume.)
2. Molar Conductivity: The conductivity of a solution per mole of electrolyte. It accounts for the number of ions. (Trend: Molar conductivity increases upon dilution. Ions are farther apart, reducing interference and increasing their mobility.)

Strong Electrolytes: Dissociate completely. Molar conductivity increases slightly and linearly with dilution. We can extrapolate to find the limiting molar conductivity.

Weak Electrolytes: Dissociate partially. Molar conductivity increases steeply at low concentrations as dissociation increases, making extrapolation impossible.

The limiting molar conductivity of an electrolyte is the sum of the individual limiting molar conductivities of its constituent ions:

Application:

We can find the limiting molar conductivity for sodium chloride:

First Law: The amount of substance produced at an electrode is directly proportional to the total quantity of electricity passed through the cell.

Second Law: For the same quantity of electricity, the amounts of different substances produced are proportional to their chemical equivalent weights.

The chemical reaction is not reversible. Once reactants are consumed, the battery is "dead."

The reaction can be reversed by applying an external current, regenerating the reactants.

Other examples include - Nickel cadmium battery, Lithium-ion batteries etc.

Unlike batteries, fuel cells don't store energy; they convert it directly as long as fuel is provided.

Case Study: The Hydrogen-Oxygen Fuel Cell

Key Advantages: 

• High Efficiency: ~70% (vs. ~40% for thermal plants).
• Pollution-Free: The only product is water.

The rusting of iron is an electrochemical phenomenon that occurs in the presence of water and air.

• Anode (Oxidation): A spot on the iron surface.
• Fe(s) → Fe²*(aq) + 2e
• Cathode (Reduction): Electrons travel to another spot where oxygen is reduced.
• O2(g) + 4H*(aq) + 4e → 2H2O(l) Final Product: Fe2+ ions are further oxidised to form rust (hydrated ferric oxide, Fe2O3 · xH2O)

• Prevention: Understanding this process leads to prevention methods like painting, coating, or using a 'sacrificial electrode'.