SC16

Question 1

SC16a
1) Recall why a chemical cell eventually stops producing a voltage.
2) Recall the main features of a hydrogen–oxygen fuel cell.

Answer 1

1) Reactions stop once reactants are used up. The limited amount of reactants are used in irreversible reactions. This means that once the reactants are used up, all reactions will stop. The cells no longer produce charge, therefore the battery must be replaced.
2) Hydrogen-oxygen cells are fuel cells. The hydrogen-oxygen fuel cell is an alternative to rechargeable cells and batteries. The electrolyte in the cell is potassium hydroxide. Hydrogen becomes oxidised. When hydrogen is placed in the anode, it becomes oxidised into H+ ions.
Fuel cells produce a voltage as long as reactants are supplied. They use hydrogen and oxygen as reactants, and water is the only product.

Question 2

SC16a
1) What is a fuel cell?
2) What should be considered when evaluating a fuel cell?
3) Explain how the voltage of a hydrogen oxygen fuel cell changes over time

Answer 2

1) A fuel cell is a device that generates electricity by using a chemical reaction to convert fuel and oxygen into electricity, heat, and water. It’s like a battery, but instead of being charged up, it’s continually supplied with fuel and air to keep producing electricity.
2) In evaluating the use of fuel cells, the following should be considered:
The impact on the environment – emissions from the cell as it is used and emissions when the fuel is produced
The impact on the user – cost, how well it works, how long the fuel cell can run without refuelling, how it compares with existing technology
3) The voltage remains constant, and produces a voltage as long as reactants are supplied

Question 3

SC16a
1) What are the advantages of hydrogen-oxygen fuel cells (state 4)?
2) What are the disdvantages of hydrogen-oxygen fuel cells (state 3)?

Answer 3

1) The advantages include:
- A fuel cell produces a voltage as long as the reactants are supplied
- Fuel cells have a longer lifetime than chemical cells
- The voltage in a fuel cell is constant, while the voltage drops in chemical cells as reactants are used up
- Water is the only product
2) There are disadvantages to using hydrogen-oxygen fuel cells in cars. These include:
- Hydrogen is in the gas state at room temperature and pressure, so it is difficult to store in the car
- Hydrogen gas is more flammable than petrol
- Fuel cells are expensive to manufacture