Redox 2 Intro Flashcards
Redox reaction
Where one element is oxidised and loses electrons…
Which is gained by another species to gain these electrons
A disproportionation reaction
The simultaneous oxidation and reduction of the same chemical
species (atom, ion, molecule or compound).
Half cells
An equilibrium system consisting of a solid metal in a solution of its own ions
What do Half cells for do?
Contain a pure metal/ gas in equilibrium with a solution of its ions
Will lose/gain electrons to release ions in solution and accumulate as
What do half cells for metals do?
Metal atoms lose electrons which accumulate on metal electrode
So releases metal cations into solution
Metal cations accumulate on surface of electrode and regain electrons to form metal atoms
Sets up equilibrium
Why do metal cations accumulate on the surface of an electrode?
Because of electrostatic attraction between positive metal ions in solution and electrons coating electrode
Electrode potential
A measure of the equilibrium position for a half-cell / electrode
Equilibrium for half cells by convention is always written….
Showing the reduction equation
Electrons are on the left hand side
An electrode potential (where the equilibrium is) that lies to the left….
Shows the element tends to be oxidised more
More likely to lose electrons and form ions
An electrode potential (where the equilibrium is) that lies to the right….
Shows the element tends to be reduced more
More likely to gain electrons
What can we use as a measure of electrode potential rather than working out the actual position of equilibrium?
By calculating a ‘standard electrode potential’ by connecting the half cell to a standard hydrogen electrode
Standard electrode potential
The potential difference measured between a half cell when it is connected to the standard hydrogen electrode under standard conditions (100 kPa, solutions 1moldm-3, 298K)
A measure of the difference in POE between hydrogen electrode and half cell
What is the standard hydrogen electrode?
A reference electrode consisting of 100kPa H2 gas, 1 moldm-3 H+ solution and a Pt electrode which has an electrode potential of 0V
Why does the standard hydrogen electrode work as a reference?
By connecting it to a half cell:
Because its voltage is 0. So the potential difference measured is equal to the half cell’s ‘standard electrode potential’
This means we can compare the standard electrode potentials of other half cells, by comparing its relative difference to SHE
When do we get a negative reading for a half cell when connected to the standard hydrogen electrode?
If the half cell we connect has an equilibrium that lies to the left meaning it is more likely to donate electrons (SO THIS HALF CELL IS OXIDISED)
And the SHE’s equilibrium lies more to the right meaning it is more likely to accept electrons (SO SHE IS REDUCED)
Half cell will be more negative than 0 aka any neg number
When do we get a positive reading for a half cell when connected to the standard hydrogen electrode?
If the half cell we connect has an equilibrium that lies to the right meaning it is more likely to accept electrons (SO THIS HALF CELL IS REDUCED)
And the SHE’s equilibrium lies more to the left meaning it is more likely to donate electrons (SO SHE IS OXIDISED)
Half cell will be more positive than 0 aka any pos number
When drawing cell diagrams/ short hand cell notation where is SHE regardless of whether it is oxidised or reduced?
By convention is shown on the left hand side
Electrochemical cell
When 2 half cells (with different electrode potentials) are connected to each other in a redox reaction to produce a potential difference
Electromotive force
Measure of the voltage of an electrochemical cell
