Hydrogen Fuel Cells (Cambridge (CIE) O Level Chemistry): Theory 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.

The table gives information about three fuels that can be used to power a car.

Use the table to give one advantage of hydrogen over petrol as a fuel for a car, other than the products formed.

Use the table to explain why hydrogen is much harder to store in a car than petrol is.

A petrol engine and a hydrogen–oxygen fuel cell both produce water.

Explain why only the petrol engine causes air pollution.

Ethanol is made from sugar cane.

Explain why ethanol is described as a renewable fuel.

The table shows that hydrogen can be obtained either from water or from natural gas.

Explain why only one of these two routes can make hydrogen a renewable fuel.

Suggest one reason why most cars still use petrol rather than a hydrogen–oxygen fuel cell.

A filling station sells hydrogen for cars powered by hydrogen–oxygen fuel cells.

The station makes its own hydrogen by the electrolysis of water.

Name the two products of the electrolysis of water.

The electricity used for the electrolysis comes from a wind farm.

Explain why the hydrogen sold at this station can be described as a renewable fuel.

State and explain one disadvantage of storing a large amount of hydrogen at the filling station.

Even when its hydrogen is made using electricity from a wind farm, a fuel cell car cannot be described as completely carbon neutral.

Suggest two reasons why.

A hydrogen filling station costs much more to build than a petrol filling station.

Suggest why this slows down the change from petrol cars to fuel cell cars.

The filling station stores hydrogen but does not store oxygen.

Explain why the cars do not need to be supplied with oxygen.

A railway company replaces a diesel train with a train powered by fuel cells.

State the two substances that the fuel cells use.

Name the only chemical product they form.

Explain why the fuel cell train produces no carbon dioxide while it is running.

Give two advantages of the fuel cell train compared with the diesel train, other than the absence of carbon dioxide.

Suggest one disadvantage of the fuel cell train compared with the diesel train.

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.

Explain why a fuel cell running on methanol is less useful than one running on hydrogen for reducing air pollution in a city.

The reaction of hydrogen in the fuel cell is described as an oxidation.

Explain, in terms of oxygen, why this reaction is described as an oxidation.

The Gemini and Apollo moon probes used hydrogen fuel cells to generate an electric current. The water produced could be used to supplement the drinking water for the astronauts.

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.

State what is supplied to each electrode, and 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.

On the Apollo spacecraft the crew cabin was a sealed environment.

Explain why a hydrogen fuel cell could be used safely inside a sealed cabin, but a petrol engine could not.

A taxi company runs two taxis. One has a petrol engine. The other is powered by a hydrogen–oxygen fuel cell.

The fuel cell operates at a much lower temperature than the petrol engine does.

Suggest how this lower operating temperature reduces one air pollutant produced by cars.

Both taxis produce water.

Explain why only the fuel cell taxi is described as non-polluting.

In the fuel cell, the hydrogen is oxidised.

Explain, in terms of electrons, what happens to the hydrogen and what happens to the oxygen.

The fuel cell taxi converts more of the energy stored in its fuel into movement than the petrol taxi does.

Explain why.

State and explain one disadvantage of running the fuel cell taxi rather than the petrol taxi.

A delivery company is deciding whether to replace its diesel vans with vans powered by hydrogen–oxygen fuel cells.

A manager writes:

> Fuel cell vans are better for the environment because they produce water.

Explain why this statement is not a complete answer.

A fuel cell van can travel further than a diesel van carrying the same mass of fuel.

Explain why.

The company is told that the vans are "zero emission".

The hydrogen for the vans is manufactured by reacting natural gas with steam.

Explain why the description "zero emission" is misleading.

Suggest two reasons, other than cost, why the company might decide not to replace its diesel vans with fuel cell vans.

The reaction between hydrogen and oxygen in the fuel cell is exothermic.

Use ideas about bond breaking and bond forming to explain why this reaction is exothermic.

Two cars are compared over the whole of their working lives. One has a petrol engine. The other is powered by a hydrogen–oxygen fuel cell.

A student writes:

> Hydrogen is a safer fuel than petrol because it does not produce carbon dioxide.

Explain why this reasoning is wrong.

Both cars produce water while they are being driven.

Explain why only the petrol car pollutes the air.

The fuel cell car is clean to drive, but over its whole life it cannot be described as carbon neutral.

Give two reasons why not.

Explain why a hydrogen–oxygen fuel cell converts a greater proportion of its fuel's energy into movement than a petrol engine does.

State and explain one reason, based on the physical state of hydrogen, why hydrogen is harder to store in a car than petrol is.