Hydrogen Fuel Cells (Cambridge (CIE) O Level Chemistry): Exam Questions

A fuel cell produces electrical energy by the oxidation of a fuel by oxygen. The fuel is usually hydrogen but methane and methanol are two other fuels which may be used. A diagram of a hydrogen fuel cell is given below.

When the fuel is hydrogen, the only product is water.

What additional product would be formed if methane was used?

Write the equation for the chemical reaction that takes place in a hydrogen fuel cell.

Fuel cells are used to propel cars.

Give two advantages of a fuel cell over a gasoline-fuelled engine.

Some cars use hydrogen–oxygen fuel cells as a source of energy.

Explain one advantage to the environment of using a hydrogen–oxygen fuel cell instead of a petrol engine.

Fuel cells can be used with alternative fuels. One alternative fuel is the liquid fuel, methanol, CH₃OH.

Suggest an advantage of using methanol instead of hydrogen in a fuel cell to power vehicles.

When methanol reacts with oxygen in a methanol-oxygen fuel cell, carbon dioxide and water are produced. Draw the reaction pathway diagram for the reaction on the axes below.

Label the following:

• reactants

• products

• activation energy

• overall energy change

Write the balanced symbol equation for the reaction between methanol and oxygen in a methanol-oxygen fuel cell.

A fuel cell produces electrical energy by the oxidation of a fuel by oxygen. The fuel is usually hydrogen but methane and methanol are two other fuels which may be used. A diagram of a hydrogen fuel cell is given below in Figure 1.

Figure 1

When the fuel is hydrogen, the hydrogen is oxidised to form water, which is the only product.

Suggest what additional product would be formed if methanol was used.

Give the chemical equation for the reaction that takes place in a hydrogen fuel cell.

In a hydrogen fuel cell, hydrogen loses electrons at the anode.

Write the half equation to show the reaction at the anode.

Hydrogen and oxygen can also react in a combustion reaction forming water vapour.

Calculate the mass of water vapour produced when 500 cm³ of hydrogen combusts in excess oxygen.

Mass of water vapour ...................................... (g)

The Gemini and Apollo moon probes use hydrogen fuel cells to generate an electric current and do not need to be electrically recharged. The product of this reaction can be used to supplement the drinking water for astronauts.

Deduce the half equations for the reactions at each electrode in a hydrogen fuel cell, and then the overall equation for the hydrogen-oxygen fuel cell, to show the product used to supplement drinking water.

A hydrogen fuel cell is an electrochemical device that converts chemical energy into electrical energy. A continuous supply of fuel is supplied to one electrode and a continuous supply of air is supplied to the other electrode.

Suggest why a fuel cell does not need to be recharged.

The General Motors Electrovan was built in 1966. It was the first vehicle powered by a hydrogen fuel cell and could travel at up to 70 mph for 30 seconds.

Suggest two environmental advantages of using a hydrogen fuel cell rather than an internal combustion engine.

Hydrogen fuel cells are commonly considered to be carbon neutral by the general public because they do not release any carbon dioxide or other greenhouse gases when they are used. This is not technically correct.

Suggest why hydrogen fuel cells cannot be classed as carbon neutral.