Electrochem Notes

Types of Electrochemical Cells

Galvanic/Voltaic Cells

Thermodynamically favored rxn
- delta G < 0
- K > 1 (proceeds to products)
produce electricity
positive electric potential

Electrolytic Cells

Thermodynamically unfavored reaction
- delta G > 0
- K < 1 (reactant favored)
power source supplies electricity to drive the rxn
negative electric potential

Porous Disk/Salt Bridge

The Porous Disk serves to allow ions to move between solutions to balance charge
Salt Bridge serves same purpose

Anode + Cathode

Remember ANOX and REDCAT
- anode → oxidation
- cathode → reduction

Standard Cell Potentials

Memorize Standard Conditions

1 atm
25 C
1.00 M

Nonstandard Conditions

Galvanic Cells

If Q > 1, rxn is CLOSER to equilibrium and E_cell < E⁰cell
- more products means less remaining electrons to flow over
If Q < 1, rxn is FURTHER from equilibrium and E_cell > E⁰cell

Electrolytic Cells

If Q > 1, rxn is FARTHER from equilibrium and |E_cell| > |E⁰cell|
If Q < 1, rxn is CLOSER to equilibrium and |E_cell| < |E⁰cell|

In the context of electrochemical cells, particularly electrolytic cells, the reaction quotient (Q) plays a crucial role in determining the position of the reaction relative to equilibrium. When Q > 1, it indicates that the concentration of products is greater than that of the reactants, pushing the reaction further away from the equilibrium state. As a result, the cell potential (Ecell) will be greater than the standard cell potential (E^0cell) in absolute value.

This means that the electrochemical reaction needs to overcome a greater energy barrier to proceed, requiring additional energy input to drive the reaction forward. The energy supplied by an external power source (like a battery or power supply) must not only account for the inherent activation energy of the reaction, but also to compensate for the unfavorable spontaneous tendency suggested by Q being greater than 1. In summary, a higher value of Q indicates a more unfavorable reaction direction, thus resulting in a higher required cell potential to achieve the desired reaction in electrolytic cells.