Redox & Electrode Potentials 5.2.3 Flashcards
How do you write Redox equations in acidic conditions?
1) Write Half equations.
2) Balence the Half Equations with each other (same number of e- in both).
3) Combine the half equations.
4) Simplify the equation.
5) Add an equal number of H+ to each side so that all OH- on Rhs becomes water.
How do you write Redox equations in Alkali conditions?
1) Balence in acidic conditions
2) Neutralis H+ on LHS by adding OH-
3) Cancel out if possible
What is a Half-Cell?
Half of an electrochemical system
What is the usual Half-Cell?
A piece of metal dipped into an aquesous solution of its ions
What is a Platinum Electrode?
A half-cell that uses a platinum electrode due to being a good catalyst, conductive and very unreactive
What is a Gas Electrode?
A half-cell using generaly Chlorine (due to its reactivity). The gas is contained with in a open bottom closed top tube, which is kept at 1atm.
A platinum electrode is half submerged and half open to the gas
What is the Standard Hydrogen Electrode?
A gas electrode which is used as a base point for all other half-cell p.d’s.
How is the p.d of a Half-Cell measured?
A p.d cannot be measured using a single half-cell.
They are measured by connecting it to a Standard Hydrogen Electrode, as they are the base point of the scale at 0V.
Why is a Salt bridge needed between the two Half-Cell solutions?
To complete the circuit and allow a current to flow, thsu creating a p.d
What does a large positve p.d mean in the Electrochemical Series?
The Chemical is a better oxidising agent.
better at losing electrons
How is the Electrochamical Series written?
Most powerful oxidising agent at the top
Least powerful oxidising agent at the bottom
All the equations are written as reductions
Which Half-Cell is Oxidised and Which is Reduced?
The more negative half-cell is oxidised
The more positive half-cell is reduced
What is the equation fo rthe overall p.d of a pair of Half-Cells?
EΘ = EΘ(Pos) - EΘ(Neg) EΘ = the overall p.d of the half-cell (effectivly the difference) EΘ(Pos) = the p.d of the more positive half-cell EΘ(neg) = the p.d of the more negative half-cell
How do you use Half-Cell values to work out if a substance can reduce another?
1) Write the entire balenced equation of the reaction
2) Split the equation into two half equations
3) Summ the p.d of the two cells
If the final answer is positive it can react
What are Limitaions of calculating the feasability of a reducing agent?
The predictions are only valid at RTP.
A high activation energy can cause the reaction ot happen slowly.
Standard electrode potenials only apply to aqueous equalibria
