Topic 20: Electrode Potentials Flashcards
Electrode potential
The voltage produced when a standard half-cell is connected to a standard hydrogen cell under standard conditions
More negative electrode potential
Better reducing agent
More positive electrode potential
Better oxidising agent
Standard hydrogen electrode elecrode
Platinum electrode
Standard hydrogen electrode pressure
100KPa
Standard hydrogen electrode temp
298K
Standard hydrogen electrode conc
1moldm^-3 HCl (H+ in solution)
Requirements of Standard hydrogen electrode
- Pt electrode
- 1 moldm^-3 conc. HCl (H+ in solution)
- 298K
- 100KPa
(H2 gas bubbled in)
Why use HCl for standard hydrogen electrode as solution?
Completely ionises (dissociates) in water as it is a strong acid, so the H+ can be used to set up the equilibrium of the reaction.
What connects two half cells?
- Wire for electrons to pass through (connect V to measure EMF)
- Salt bridge for ions to move between the cells to complete the circuit
Salt bridge made of
Paper soaked in KNO3 solution potassium nitrate
EMF
Erhs - Elhs
(more positive) - (more negative)
Meaning in convential representation of cells |
Phase boundary, only between different states
Oxidised/ reduced in conventional representation of cells
Most oxidised closest to the middle
Most reduced further away
ROOR
So one being reduced on the right one being oxidised on the left
Hydrogen always goes on the left and include Pt
Salt bridge in conventional representation of cells
||
Why is Pt used for half cells with no solid
- unreactive
- metal so conducts electricity
, Meaning in convential representation of cells
Between same state
Electrode potential of H
0V
Feasible EMF reaction
Positive EMF means feasible rxn
Non- rechargeable cells advantages
- Cheaper
- Easy to use
- Portable easy to replace
- Work in wide range
Non- rechargeable cells disadvantages
- Waste
- Leakages can occur
- Non-sustainable
- Toxic chemicals from landfill get into water
Rechargeable batteries
Reversible reactions - check if need to know equations
Rechargeable batteries advantages
- More energy efficient as charging takes less energy than making new batteries
- Longer life-span than non-rechargeable
- Recharged multiple times
- Can last longer on single charge than nr
Rechargeable batteries disadvantages
- Cost more
- Need to be recharged regularly
- Non all appliances work with them
- Will eventually degrade
