C6 - Fuel Cells

Question 1

What are fuel cells?

Answer 1

Fuel cells use the heat energy generated by the reaction between hydrogen and oxygen to create electrical energy.

Question 2

What does hydrogen react with in a fuel cell?

Answer 2

Oxygen from the air.

Question 3

Why is the reaction in a fuel cell exothermic?

Answer 3

Because energy is released during the reaction.

Question 4

Why is the reaction efficient?

Answer 4

It is an efficient reaction because the energy released can be converted into electrical energy.

Question 5

What acts as fuel in the fuel cell?

Answer 5

Hydrogen is the fuel in a fuel cell.

Question 6

What is the word equation for a hydrogen fuel cell reaction?

Answer 6

hydrogen + oxygen = water

Question 7

What are fuel cells used for?

Answer 7

They are used to produce electric current in spacecrafts and small vehicles.

Question 8

Why are fuel cells used in spacecrafts?

Answer 8

• they are efficient and waste little energy
• the water produced is not wasted (astronauts drink it)
• there are no moving parts
• they can be used continuously
• they are compact

Question 9

A normal car engine converts chemical energy into heat, and the heat is converted into movement energy. Why is this dangerous?

Answer 9

This is dangerous because the temperature gets hot enough to react with the nitrogen and oxygen in the air and causes nitrous oxides which cause smog.

Question 10

Why do fuel cells produce less pollution?

Answer 10

They produce less pollution because they do not burn fossil fuels or produce carbon dioxide.

Question 11

What are the advantages to fuel cells?

Answer 11

• energy is converted directly from chemical energy into electrical energy
• fewer transfer stages so less energy losses
• more efficient as almost all the energy is converted
• less pollution
• less fuel consumption as they are lighter

Question 12

What are the disadvantages to fuel cells?

Answer 12

• they use poisonous catalysts which will have to be disposed of at the end of the life time of the cell
• they involve the use of energy which may come from burning fossil fuels

Question 13

What is the waste gas in a hydrogen/oxygen reaction?

Answer 13

Water vapour.

Question 14

What does the squeaky pop test check for?

Answer 14

Hydrogen gas.

Question 15

What is the balanced symbol equation for a hydrogen fuel cell?

Answer 15

2H2 + O2 = 2H2O

Question 16

What is the ionic equation for hydrogen forming ions at the cathode?

Answer 16

2H2 = 4H+ + 4e-

Question 17

At the negative electrode, the hydrogen releases an electron. What type of reaction is this?

Answer 17

This is an oxidation reaction.

Question 18

If the ions are lost and the anode gains electrons, what type of reaction is this?

Answer 18

This is a reduction reaction.

Question 19

What is the symbol equation for a reduction reaction in fuel cells?

Answer 19

4H+ + O2 + 4E- = 2H2O

Question 20

What is a redox reaction?

Answer 20

A redox reaction is where electrons are both gained and lost.

Question 21

What happens to the amount of chemical energy in a reaction that gives out heat?

Answer 21

The amount of chemical energy decreases.

Question 22

The fuel in a fuel cell is oxidised. Use one of the half equations to explain why.

Answer 22

It gains electrons meaning it is a reduction reaction. Therefore it has been oxidised. 4H+ + O2 + 4e- = 2H2O