Storage and Fuel cells

Question 1

What are the three types of storage cells?

Answer 1

• primary
• secondary
• fuel cells

Question 2

What are primary cells?

Answer 2

• non - rechargeable and are designed to be used once
• when used, the electrical energy is produced by oxidation and reduction at electrodes
• these reactions can not be reversed
• eventually, the chemicals are used up and the voltage cell goes flat and the cell is discarded
• this is used in low current storage devices like smoke detectors

Question 3

Write an equation of zinc and manganese and a potassium hydroxide alkaline electrolyte?

Answer 3

Cell reaction : Zn (s) + 2MnO2 (s) = ZnO (s) + Mn2O3 (s)

Question 4

What are secondary fuel cells?

Answer 4

• secondary cells are rechargeable
• unlike primary cells, the reactions producing electrical energy can be reversed. The chemicals can be regenerated and the cell can be used again

Question 5

What are the common examples of fuel cells?

Answer 5

• lead batteries, used in radios and torches

Question 6

What occurs in charging a secondary primary cell?

Answer 6

• the more negative electrode is oxidised and the more positive electrode is reduced

Question 7

What occurs in recharging a secondary primary cell?

Answer 7

• the electrode that was reduced is charging and is now oxidised
• the electrode that was oxidised is now reduced

Question 8

Evaluate a secondary primary cell?

Answer 8

Benefits = cheap to make, have a relatively high power density

Risks = production involves toxic chemicals, disposal is expensive and some cells are only used once, increasing waste

Question 9

What is a fuel cell?

Answer 9

A fuel cell uses the energy from the reaction of a fuel with oxygen to create a voltage
The flow of oxygen and fuel into the fuel cell and the products. The electrolyte remains in the cell
The fuel cell operates continuously provided that fuel and oxygen are supplied into the cell, fuel cells therefore do not need to be recharged

Question 10

What are the reactions of alkaline hydrogens fuel cell and the overall reaction.

Answer 10

Oxidation = H2 (g) + 2OH- (aq) = 2H20 (l) + 2e-
Reduction = 1/2O2 (g) + H2 (g) = H20 (l)

Overall = 1/2O2 (g) + H2 (g) = H20 (l)

Question 11

What is the process of an alkaline hydrogen fuel cell?

Answer 11

Hydrogen diffuses in and reacts with the OH- eletrolyte, forming water and 2 electrions
The electrons then travel across the wire, creating voltage
The oxygen then reacts with water and 2 electrons, reforming OH- and then OH- diffuses back into electrolyte

Question 12

What is the process of an acid hydrogen fuel cell?

Answer 12

• At the anode = H2 splits into H+ and electrons
• H+ travels across electrolytes and forces e- to travel around the circuit
• At the cathode = Oxygen reacts with H+ and electrons and forms H20 which travels out of the fuel cell

Question 13

What are the reactions of acid hydrogens fuel cell and the overall reaction.

Answer 13

Oxidation = H2 (g) = 2H+ (aq) + 2e-
Reduction = 1/2O2 (g) + 2H+ (aq) + 2e- = H20 (l)

Overall = 1/2O2 (g) + H2 (g) = H20 (l)