C7 Energy Changes

Question 1

How is electricity made in batteries?

Answer 1

By placing 2 different metals in an electrolyte solution

Question 2

What is an electrolyte solution?

Answer 2

A solution that can conduct electricity, e.g. a molten ionic compound

Question 3

On what condition can cells produce electricity?

Answer 3

If they use metals with different reacitivity

Question 4

How can the potential difference be changed in a cell?

Answer 4

By increasing/decreasing the difference in reactivity between the metals, you increase/decrease the potential difference.

Also the electrolyte can affect the potential difference

Question 5

What is a battery?

Answer 5

2 or more cells connected in series to produce a greater voltage

Question 6

Why can rechargable batteries be recharged?

Answer 6

The chemical reactions can be reversed when applying an electrical current

Question 7

How do fuel cells produce electricity?

Answer 7

A fuel e.g. hydrogen is reacted with pure oxygen or air

Question 8

What waste product is produced in a hydrogen fuel cell?

Answer 8

Water

Question 9

What’s the half equation at the negative electrode in a hydrogen fuel cell?

Answer 9

2H₂ —- 4H⁺ + 4e⁻

Question 10

What’s the half equation at the positive electrode in a hydrogen fuel cell?

Answer 10

2O2⁻ → O2 + 4e-

Question 11

What is happening to the hydrogen inside the hydrogen fuel cell?

Answer 11

It’s being oxidised (gaining oxygen)

Question 12

What is the overall equation inside a hydrogen fuel cell?

Answer 12

O₂ + 2H₂ —– 2H₂O

Question 13

What are some advantages of Hydrogen fuel cells compared to rechargable batteries?

Answer 13

• They produce energy as long as hydrogen is present
• They don’t get less efficient the longer they run
• Can be used as a source of drinking water
• Can be used to replace fossil fuels as they don’t
  release greenhouse gases

Question 14

What are some disadvantages of rechargable batteries compared to hydrogen fuel cells?

Answer 14

• They run out and need to be recharged

- They store less electricity the more charging cycles they go through and eventually need to be replaced

Question 15

What are some disadvantages of Hydrogen fuel cells compared to rechargable batteries?

Answer 15

• Hydrogen is an explosive gas and is difficult to store

- They produce a relatively low voltage

Question 16

What are some advantages of rechargable batteries compared to Hydrogen fuel cells?

Answer 16

• They can produce a larger voltage

- No dangerous fuels are required for them

Question 17

Explain how Hydrogen fuel cells produce electricity

Answer 17

As fuel enters the cell, it become oxidised, setting up a potential difference across the cell

Question 18

Hydrogen fuel cells can be used to power different forms of transport.
Some diesel trains are being converted to run on hydrogen fuel cells.
A newspaper article referred to the converted trains as the new ‘steam trains’.
Suggest why.

Answer 18

• In a fuel cell hydrogen is

oxidised and water is produced

Question 18

Hydrogen fuel cells can be used to power different forms of transport.
Some diesel trains are being converted to run on hydrogen fuel cells.
A newspaper article referred to the converted trains as the new ‘steam trains’.
Suggest why.

Answer 18

• In a fuel cell hydrogen is

oxidised and water is produced