Topic 14 Redox Equilibrium Flashcards
(26 cards)
Steps to set up an electrochemical cell (5 steps)
- Obtain and clean metal with sandpaper (+ gloves)
- Clean grease from surface with propanone and wear gloves
- Place each metal into a solution containing the ion of the same metal
(Add acid for oxidising agents)
4.Make salt bridge from filter paper and KNO3 (or KCl) and put it in each beaker not touching electrodes - Connect electrodes with wires and a voltmeter
What are the two types of half cell
Metal electrode in its own ions or platinum electrode with 2 aqueous ions
Why is a platinum electrode used for solutions containing two aqueous ions
Inert and conductive
Where do electrons flow from and to in terms of reactivity
From a more reactive metal to a less reactive metal
What is electrode potential
How easily half cells give up electrons (are oxidised)
What does NO PRoblem stand for
Most Negative half cell is Oxidised
Most Positive half cell is Reduced
What is the SHE and what is it used for
Standard hydrogen electrode. Used as a reference to measure standard electrode potentials
What is the set up of the SHE
Pt electrode, 1 mol dm-3 H+ and H2(g) in at 298K, 100 kPa
3 Standard conditions of SHE?
- 298K
- 100kPa
- 1 mol dm^-3 conc H+
Formula for standard cell potential
E reduced - E oxidised
E right - E left
E most positive - E most negative
3 things affecting half cell potential
- Temp
- Conc
- Pressure
Cell notation acronym
ROOR - R - reduced state O - oxidised state
Cell notation rules (4)
- Negative half cell left positive right
- Reduced form Oxidised form Oxidised form Reduced form
- Single line for state change double line for salt bridge
- Comma to separate substances in same state (don’t forget Pt electrode)
When is a reaction feasible in electrochemical cells
E cell > 0 or do NO PRoblem and see if the equation formed matches the question
When may a feasible reaction not occur (3)
- non standard conditions
- slow rate of reaction
- activation energy too high
What is E cell directly proportional to
Total entropy change and the natural log of the equilibrium constant (lnk)
How do rechargeable batteries work
When a current is supplied the discharge equation is reversed
What two substances react in a lithium ion battery
Lithium and Cobalt (IV) Dioxide
What do fuel cells need to generate electricity
A continuous external supply of chemicals
Ox and Red Formula in alkaline hydrogen fuel cell
OX 2H2 + 4OH- —> 4H2O + 4e-
RED O2 + 2H2O + 4e- —> 4OH-
General formula for hydrogen fuel cells
O2 + 2H2 —> 2H2O
Electrolyte in alkaline fuel cells
KOH to carry OH-
Two other hydrogen rich molecules used in fuel cells? And how do they create hydrogen from them
Methanol and ethanol release hydrogen using a reformer
Why is a salt bridge used
To complete the circuit and balance charges
