Topic 3 Flashcards
Disproportionation reaction
An element in a single species is simultaneously oxidised and reduced
Oxidation number of oxygen:
Normally
In peroxides
With fluorine
Normally -2
In peroxides -1
With fluorine +2
When describing oxidation numbers in reactions
Oxidation number changes from x to y
So element has gained/lost electrons
So is reduced/oxidation
Electrode potential definition
E°
The potential difference of the half cell relative to the standard hydrogen electrode
What are standard conditions?
Temperature= 298K
Pressure of gasses= 100kPa or 1atm
Concentration of ions= 1.00 mol dm-3
Why do you need two electrodes to measure the electrode potential?
A voltmeter needs two connections
But introducing a new metal electrode in the same solution would set up its own potential difference
Why is it important for standard conditions to be used?
The reactions are in equilibria, so the position of equilibrium varies with the conditions.
If reduction favoured- electrode potential more positive.
If oxidation favoured- electrode potential more negative.
What is the salt bridge needed for?
Allows movement of ions, needed to complete the electrical circuit
What does the salt bridge contain?
Concentrated solution of potassium nitrate or sodium chloride
Equation for Emf (electromotive force)
Emf = E right (more +ve) - E left (more -ve)
Why might a reaction that is thermodynamically feasible not take place?
The activation energy is too large- the reactants are kinetically stable
Or if it is not under standard conditions
What is the relationship between entropy and E cell?
ΔS total = E cell
What is the relationship between the equilibrium constant and E cell?
ln K ∝ E cell
How does the Ecell tell you if the reaction is feasible?
If the E cell is positive, the reaction is feasible
