Electrochemical Cells/Voltaic Cells Flashcards
What is an electrochemical/voltaic cell?
A voltaic cell uses a redox reaction to generate electricity, the oxidation and reduction reactions are carried out in separate half cells.
What are the two half cells linked by, and what does this help?
The two half cells are linked by a salt bridge, this prevents build up of charge in one half cell and completes the circuit.
It is made from paper dipped in KNO3 solution.
Why is the salt bridge formed with KNO3 solution?
Since KNO3 solution is soluble and allows the ions to flow freely, preventing a build up of charge in one half cell and completing the circuit
What does NO PR stand for?
NO = Negative, oxidation
The most negative E standard value is where oxidation occurs
PR = positive, reduction
The most positive E standard value is where reduction occurs
How do you answer a voltaic cell Q?
- draw a scale with the two E standard values
- mark on NO and PR
- work out which half equation becomes reversed (always NO)
- write out the correct half equations
- write the overall cell equation (adding two half equations)
- calculate the cell potential (most positive E standard value - most negative E standard value)
What is the E standard overall cell potential also?
It is also the maximum voltage that can be produced by the cell
If a half cell involves two aqueous ions what is the electrode made from?
It is made from an inert metal such as platinum
What are the standard states and conditions for a voltaic cell?
- 298K
- 1 atm
- 1 moldm-^3 of each solution
What is the standard hydrogen electrode?
You cannot measure the potential of a half cell so all potentials are relative to the standard hydrogen electrode
E standard value : 0.00V
Reaction: 2H+ (aq) + 2e- => H2(g)
Conditions: 298K, 1 atm, 1M conc
What is E standard?
The potential difference between the half cell and a standard hydrogen electrode
What is an oxidising agents E standard value like?
An oxidising agent themselves are reduced so have a very positive E standard value.
The best oxidising agent will have the most positive E standard value and be on the LHS of the chart.
What is a reducing agents E standard value like?
Reducing agents are themselves oxidised so have a very negative E standard value.
The best reducing agent will have the most negative E standard value and will be on the RHS of the chart.
What is a e standard cascade?
If one reactant is present in excess it may trigger multiple redox reactions. Use NO PR to predict final products.
What is the MAGIC SENTENCE for predicting spontaneity?
The E standard value for X+/X is more (negative/positive) than the E standard value for Y+/Y so it is able to (oxidise/reduce) Y+ into Y.
