CELL POTENTIAL (Ecell)
- Difference in electrical potential of electrodes.
- Also called voltage or electromotive force (emf).
- Cell emf depends on the concentration of ions in the cell, the temperature of solutions and pressure of gasses involved.
· Unit : Volt (V).
Ecell > 0 | Ecell = 0 | Ecell < 0 |
Spontaneous cell reaction. | Reaction has reach equilibrium. | Non spontaneous cell reaction. |
STANDARD CELL POTENTIAL (EOcell)
- Difference in electrical potential of electrodes measured at specified temperature (usually 298 K) with all components in their standard state which are :
- 1 atm (for gases)
- 1M for solutions
- Pure solid for electrodes
Eocell = Eocathode - Eoanode
· STANDARD ELECTRODE (HALF-CELL) POTENTIAL (EOhalf-cell)
- Potential associated with a given half reaction (electrode compartment) when all components are in their standard states.
- Also called standard reduction potential.
- Changing the balancing coefficients of a half-reaction does not change Eo value because electrode potentials are intensive properties.
- Eg. :
Oxidation (anode) : Zn(s) → Zn2+(aq) + 2e- Eoanode = -0.76 V
Reduction (cathode) : Cu2+(aq) + 2e- → Cu(s) Eocathode = +0.34 V
Overall : Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
Eocell = Eocathode - Eoanode
= Eocopper - Eozinc
= +0.34 V – (-0.76 V)
= +1.10 V
STANDARD HYDROGEN ELECTRODE (SHE)
- SHE is the standard reference electrode to measure the electrode potentials of other half-cell.
- SHE is assign as zero potential (0 V)SHE consists of H2 gas at 1 atm,25°C bubbling around a platinum electrode which is immersed in 1 M of solution H+.
- The electric potential of the half reaction is due to the reduction of H+ to H2 (g).
2H+ (aq) +2e-→H2 (g) E° =0.00V
STANDARD REDUCTION POTENTIAL TABLE
From the table,
- The element with more +ve E° becomes cathode.
- The element with more -ve E° becomes anode.
- The more +ve Eo favours reaction to the right.
- The more -ve Eo favours reaction to the left.
- The more +ve E° , the stronger the oxidising agent.
- The more -ve E° , the stronger the reducing agent.
0 comments:
Post a Comment