Redox II Flashcards
Electrochemical cell basic premise
Electron exchange during collisions
Exothermic
Increased temperature
Energy released
Ecell meaning, conditions
Change in pd
Value = change in redox reaction
Symbol = change in cell polarity
100KPa, 298K, 1mol/dm3
Describe practical setup of an electrochemical cell
LHE/RHE
Beaker with salt solution and submerged solid
Salt bridge (allow anion transfer/maintain neutral net charge)
Ammeter connected between crocodile clips of two solids
Describe the respective movements occurring in a electrochemical cell
Oxidised species
More negative electrode
Electron producer
Lose electrons
Gain anions
More solution, less solid
Reduced species
Less negative electrode
Electron acceptor
Gains electrons
Loses anions
Less solution, more solid
Describe rules for writing cell diagrams
Most oxidised species goes closest to salt bridge
Separate species of different states with a line
For non metals, use a platinum catalyst, line separates catalyst from species
Can have may species within each side of the half equation of a cell diagram, use [ ] to group together
Why is platinum used as a catalyst for electrode potential data
No connection species
Electron pathway
Divided, high SA, black appearance
What is a standard reference electrode
Means of dining the Ecell of a species
Quantitative reactivity comparison can be made
Connection and measurement of one electrode of an electrochemical cell
Hydrogen standard reference electrode
H2 —>< 2H+ + 2e-
Pt [H2] I [2H+]
Connect Pt to a voltmeter
Incoming hydrogen gas
1mol/dm3 HCl solution
Ecell equation
RHE - LHE
Reduction - oxidation
Be careful of signs
Units = V
Three methods of determine direction of change
More -ve, e- producer, oxidised
+ve Ecell diagram, right direction species movement
Most -ve half equation on top, anticlockwise rule
How to get half equations from cell diagrams
Separate species with —><
Accommodate charge difference with e-
Disproportionation in Ecell direction of change
2 half equations including the same species
Apply direction of change rules
If both convert away from the same unstable species
Ecell extent of change
Ecell equivalent to deltaG
DeltaG = -nFEcell
DeltaG & -Ecell
DeltaStot & Ecell
Lnk & Ecell
What is the critical Ecell value for completion, why might this not always be the case
+0.6
Wont go fully is Eact is too high/slow
Equilibrium may go to completion outside a closed system
DeltaG/S/Ecell vary away from standard conditions
Redox titration uses
Prove a reaction works based on Ecell
Use KMnO4 for reducing agents, -ve electrodes
Use I- for oxidising agents, + electrodes
