5.2.3 Electrode Potentials

Question 1

what is standard electrode potential?

Answer 1

• the emf (voltage) of a half cell compared with the standard hydrogen half cell
• measured at 298K, solutions 1moldm-3, gases 100kPa

Question 2

what is the half cell for a solid and and aqueous ions?

Answer 2

• metal solid in solution

Question 3

what is the half cell for gas and aqueous ions?

Answer 3

• Pt metal
• hydrogen gas (see notes)

Question 4

what is the half cell for 2 aqueous solutions?

Answer 4

• Pt metal
• both aqueous solutions

Question 5

what else needs to be drawn in an electrochemical cell drawing?

Answer 5

• salt bridge
• voltmeter

Question 6

why is platinum used?

Answer 6

• inert electrode

Question 7

what is a salt bridge?

Answer 7

• filter paper soaked in an inert soluble substance e.g. potassium nitrate
• it allows ions to flow but not electrons

Question 8

what is the electrode potential of hydrogen?

Answer 8

0V

Question 9

which is the positive terminal?

Answer 9

• the cell with the more positive E0-
• the reaction will go forwards and gain electrons (reduction)

Question 10

which is the negative terminal?

Answer 10

• the cells with the more negative E0-
• the reaction will go backwards and lose electrons (oxidation)

Question 11

which way do electrons flow?

Answer 11

• negative to positive

Question 12

how to work out Ecell?

Answer 12

more positive E0- - more negative E0-

Question 13

how to predict the feasibility of a reaction?

Answer 13

• the equation with the more positive electrode potential will go forwards (gains electrons, reduction)
• the equation with the more negative electrode potential gas backwards (loses electrons, oxidation)
• state effect on position of equilibrium too

Question 14

what are the limitations of predicting feasibility?

Answer 14

• non-standard conditions
• rate too slow due to high activation energy
• larger difference in electrode potentials = less likely to take place

Question 15

when do non-rechargeable cells stop working?

Answer 15

• when the chemicals have reacted

Question 16

how are rechargeable cells recharged?

Answer 16

• cell reaction can be reversed
• e.g. lithium cells
• disadvantages: toxicity, danger of fires, need recharging

Question 17

how do fuel cells work?

Answer 17

• a fuel cell uses the energy from the reaction of a fuel with oxygen to create a voltage
• the reactants flow in and the products flow out while the electrolyte remains in the cell so they can operate continuously

Question 18

what are the advantages of fuel cells?

Answer 18

• don’t have to be recharged
• work continuously as long as there is a supply of fuel and oxidant

Question 19

Which way does the equilibrium shift?

Answer 19

• most negative system equilibrium shifts left
• most positive system equilibrium shifts right