Electrode Potentials & Fuel Cells

Question 1

What is the definition of redox?

Answer 1

A reaction in which both reduction and oxidation take place.

Question 2

What is the definition of oxidation number?

Answer 2

A measure of the number of electrons that an atom uses to bond with atoms of another element.

Question 3

What is the definition of half-reaction?

Answer 3

The reaction that takes place on one half-cell of an electrochemical cell.

Question 4

What is the definition of oxidising agent?

Answer 4

A reagent that takes electrons from another species.

Question 5

What is the definition of a reducing agent?

Answer 5

A reagent that adds electrons to another species.

Question 6

What molecules can you add to an equation in order to balance it?

Answer 6

H+, OH- & H2O.

Question 7

What is the definition of standard electrode potential?

Answer 7

The electron motive force of a half cell compared with a standard hydrogen half cell measured at 298K with solution concentrations of 1.0moldm-3 and a gas pressure of 100kPa.

Question 8

What is a standard hydrogen electrode used for?

Answer 8

Used as a reference for the measurement of voltages in electrochemical cells.

Question 9

What do ions pass through in an electrochemical cell?

Answer 9

Through the salt bridge.

Question 10

What do electrons pass through in an electrochemical cell?

Answer 10

Through the wire.

Question 11

What is the term used for the voltmeter in an electrochemical cell?

Answer 11

High resistance voltmeter.

Question 12

Which electrode releases electrons?

Answer 12

The electrode with the more negative electrode potential.

Question 13

What is the electron motive force?

Answer 13

The voltage produced by a cell when no current flows.

Question 14

What does a large difference in electrode potentials between two half cells mean?

Answer 14

That the reaction is more likely to take place.

Question 15

What is the electrode potential of a cell?

Answer 15

The difference between the standard electrode potentials of half cells.

Question 16

What is the equation for E cell?

Answer 16

E cell= E(+ve terminal) - E(-ve terminal)

Question 17

Below what voltage is a reaction unlikely to take place?

Answer 17

0.40V

Question 18

What are the limitations of predictions made using standard cell potentials?

Answer 18

They may not be standard conditions so Le Chatelier’s principle will kick in.
They may have a high activation energy.
They may not be in aqueous Equilibria

Question 19

Outline a non-rechargeable cell.

Answer 19

A cell which provides electrical energy until all the chemicals have reacted and the cell is flat and discarded.

Question 20

Outline a rechargeable cell.

Answer 20

Chemicals in a cell react to provide electrical energy and this reaction can be reversed whilst recharging so it can be used again.

Question 21

Outline a fuel cell.

Answer 21

Uses external supplies of a dual and an oxidant to produce electrical energy so long as there is a constant supply.

Question 22

Outline how a hydrogen-oxygen fuel cell works.

Answer 22

A fuel cell uses energy from the reaction of a fuel with oxygen to create a voltage.

Question 23

What do fuel cells need to operate continuously?

Answer 23

A continuous supply of fuel and oxygen.

Question 24

What are the advantages of using methanol as a fuel rather than hydrogen?

Answer 24

It is a liquid fuel which is easier to store than hydrogen gas.
Methanol can be generated by biomass.

Question 25

What are the advantages of FCVs (fuel cell vehicle) over conventional petrol or diesel powered vehicles?

Answer 25

Produce less pollution and carbon dioxide and have a greater efficiency.

Question 26

Hydrogen storage as a

Answer 26

liquid under pressure
adsorbed on the surface of a solid material
absorbed within a solid material

Question 27

What is the limitation of large scale storage & transportation of hydrogen?

Answer 27

It isn’t cost effective or energy efficient.

Question 28

Redox equations can be worked out from

Answer 28

Constructing and combining half equations

Working out oxidation states and balancing for charge

Question 29

Standard hydrogen electrodes can be connected to

Answer 29

Metals/non-metals in contact with their ions in aq solution

Ions of the same element in different oxidation states

Question 30

Reaction feasible when standard electrode potential is

Answer 30

positive

Question 31

Standard electrode potential predictions may be incorrect

Answer 31

Activation energy may be too high

May not be under standard conditions e.g. more than 1.00moldm-3 conc of solution

Question 32

Fuels cell use

Answer 32

The energy from the reaction of a fuel with oxygen to create a voltage

Question 33

Hydrogen economy may contribute to future energy needs but limitations are

Answer 33

public and political acceptance of hydrogen as a fuel
handling and maintenance of hydrogen systems
initial manufacture of hydrogen that needs energy

Question 34

Acid fuel cell

Answer 34

Oxidation - h2 → 2H+ + 2e-
Reduction - 2H+ + 1/2O2 + 2e- → h2o
Overall - 1/2O2+H2→ H2O

Question 35

Alkaline fuel cell

Answer 35

Oxidation - h2 + 2oh- → 2e- + 2h20
Reduction - 1/2o2 + h2o +2e- → 2oh-
Overall - 1/2o2+h2→h2o