ELECTROCHEM

Question 1

defn of standard electrode potential(E°)

Answer 1

electromotive force b/w the half cell and the standard hydrogen electrode, measured at standard conditions

Question 2

defn of standard cell potential (E°cell)

Answer 2

maximum potential difference between two half cells under standard conditions

Question 3

standard conditions

Answer 3

298K(25 degrees), 1 bar(100000Pa), 1 mol dm-3

Question 4

purpose of platinum black coating/porous platinum in SHE

Answer 4

increase the SA of electrode so that eqm b/w H2(g) and H+(aq) can be established quickly

Question 5

standard cell potential eqn

Answer 5

E°cell = E°cathode - E°anode

Question 6

Explain direction of e- flow from value of E°cell(more positive E°)

Answer 6

E°(MnO4-/Mn2+) is more +ve than E°(Cl2/Cl-)
MnO4- has a higher tendency than Cl2 to undergo reduction
MnO4- will undergo reduction while Cl- undergo oxidation
E- flow from Cl2/Cl- half cell to MnO4-/Mn2+ half cell

Question 7

eqn of spontaneity of rxn

Answer 7

ΔG°cell = -nFE°cell

Question 8

Explain limitations of using E°cell is making spontaneity predictions(3)

Answer 8

1) Conditions may not be in standard conditions

2)The reaction does not occur since it is not kinetically feasible since Ea is too high, thus reaction rate is too low

3)Side reactions may occur, making the reaction spontaneous despite predicting the reaction to be non-spontaneous

Question 9

Advantages of using the H2/O2 fuel cell and improved batteries compared to galvanic cells

Answer 9

1) smaller size, lower mass and higher voltage
2)produce no pollutants since water is the product
3)high efficiency in conversion of chemical to electrical energy