Chemical cells and fuel cells

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What is a chemical cell?

A chemical cell is a source of electrical energy.
It is made from two electrodes (usually metals of different reactivity) placed in an electrolyte.
The electrodes are connected by wires to an external circuit, creating a complete circuit.
The more reactive metal releases electrons more easily, giving it a negative charge.
Electrons flow through the external circuit from the more reactive electrode to the less reactive electrode.
The difference in the ability of the electrodes to release electrons produces a voltage (potential difference).

Factors affecting voltage

The type of electrode affects the voltage: the greater the difference in reactivity between the two metals, the greater the voltage.
The electrolyte also affects the voltage because different ions react with the electrodes in different ways.
Using two electrodes made of the same metal produces 0 V because there is no difference in reactivity.
You can use the reactivity series to predict the voltage: metals further apart give a larger voltage.

Cells and batteries

A battery consists of two or more cells connected in series.
Connecting cells in series adds their voltages together, giving a larger overall voltage.
For example, three 1.5 V cells connected in series produce 4.5 V.
Cells produce a voltage only until one of the reactants is used up; then the battery goes flat.

Non-rechargeable and rechargeable cells

In non-rechargeable cells, the chemical reaction stops when one reactant is used up, so no more electricity is produced.
Alkaline batteries are examples of non-rechargeable batteries.
In rechargeable cells, the chemical reactions can be reversed by supplying an external electrical current.
Reversing the reactions allows the cell to be used again.
Rechargeable cells avoid the need to dispose of batteries as often, which is better for the environment.

Hydrogen fuel cells: how they work

A fuel cell is an electrochemical cell in which a fuel donates electrons at one electrode and oxygen gains electrons at the other.
Fuel cells need a continuous supply of fuel and oxygen (or air) to keep working.
The fuel is oxidised electrochemically within the cell, producing a potential difference (voltage).
In a hydrogen-oxygen fuel cell, hydrogen is oxidised and oxygen is reduced, producing water as the only chemical product.
The overall reaction is: hydrogen + oxygen → water.
The electrolyte is often potassium hydroxide solution or phosphoric acid, and electrodes are porous carbon coated with a catalyst.

Hydrogen-oxygen fuel cell

Electrode reactions in hydrogen fuel cells (HT only)

At the anode (negative electrode), hydrogen is oxidised: 2H₂ → 4H⁺ + 4e⁻.
At the cathode (positive electrode), oxygen is reduced: 4H⁺ + O₂ + 4e⁻ → 2H₂O.
The overall reaction is: 2H₂ + O₂ → 2H₂O.
Electrons flow through the external circuit from anode to cathode, driving an electric motor.
Remember: the two half equations combine to give the overall equation.

Advantages of hydrogen fuel cells

They do not produce any pollution: the only product is water.
They produce more energy per kilogram than petrol or diesel.
No power is lost in transmission because there are no moving parts, unlike an internal combustion engine.
There are no batteries to dispose of, which is better for the environment.
They are a continuous process and keep producing energy as long as fuel is supplied.
They are quieter, so they cause less noise pollution.

Disadvantages of hydrogen fuel cells

Materials used in producing fuel cells are expensive.
High pressure tanks are needed to store hydrogen and oxygen, which are dangerous and difficult to handle.
Fuel cells are affected by low temperatures, becoming less efficient.
Hydrogen is expensive to produce and store.
They are quiet, which can be a danger to pedestrians if used in cars and lorries.

Comparing fuel cells with rechargeable cells and batteries

Fuel cells need a continuous fuel supply, whereas batteries store energy and run down.
Rechargeable batteries can be recharged by reversing the chemical reactions; fuel cells cannot be recharged.
Hydrogen fuel cells produce only water, while rechargeable batteries may contain harmful chemicals that need disposal.
Fuel cells are becoming more common in vehicles to replace petrol or diesel engines.
Hydrogen fuel cells offer a potential alternative to rechargeable cells and batteries.

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Câu hỏi luyện tập

Xem trước miễn phí — 8 trên 60 câu hỏi. Đăng ký để xem tất cả.

1.What name is given to the solution that contains ions and allows charge to flow between the electrodes in a simple cell?
Easy
- AElectrolyte
- BElectrode
- CVoltmeter
- DAmmeter
2.A simple cell is made using two copper electrodes in sodium chloride solution. The voltmeter reads 0 V. What is the explanation for this reading?
Easy
- AThe circuit is not complete
- BThe sodium chloride solution cannot conduct electricity
- CThe electrodes are made of the same metal
- DThe voltmeter is faulty
3.Three 1.5 V cells are connected correctly to form a battery. What is the total voltage produced?
Medium
- A1.5 V
- B3.4 V
- C3.0 V
- D4.5 V
4.Which of the following factors affect the voltage produced by a simple cell? (select all that apply)
Medium
- AThe type of electrode used
- BThe type of electrolyte used
- CThe size of the voltmeter
- DThe difference in reactivity of the two metals
- EThe colour of the electrolyte solution
5.Which statement about non-rechargeable cells is correct?
Medium
- AThe chemical reactions can be reversed by supplying an external current
- BThe reactions stop when one of the reactants has been used up
- CThey can be recharged many times
- DThey produce electricity indefinitely
6.Alkaline batteries are examples of non-rechargeable batteries.
Easy
True or false?
7.In a hydrogen fuel cell, hydrogen undergoes reduction at the anode.
Easy
True or false?
8.Match each substance in a hydrogen fuel cell with its function.
Medium
- Potassium hydroxide solution
- Hydrogen
- Water
- Electrolyte
- Fuel
- Waste product

Thêm câu hỏi

9.Place these metals in order of reactivity, from most reactive to least reactive, based on the voltages they produce in a simple cell with copper.
Medium
- Copper
- Tin
- Zinc
- Magnesium
10.Which of the following is an advantage of using hydrogen fuel cells in vehicles compared with petrol engines?
Medium
- AThey produce only water as a product
- BThey are cheaper to manufacture
- CThey store hydrogen easily at room temperature
- DThey work equally well at all temperatures
11.Which half equation represents the reaction at the anode in a hydrogen fuel cell?
Medium
- A2H₂ → 4H⁺ + 4e⁻
- B4H⁺ + O₂ + 4e⁻ → 2H₂O
- C2H₂ + O₂ → 2H₂O
- DO₂ + 4e⁻ → 2O²⁻
12.In a hydrogen fuel cell, the anode is the negative electrode and the cathode is the positive electrode.
Easy
True or false?
13.Match each term with its correct description.
Medium
- Chemical cell
- Battery
- Fuel cell
- Two electrodes of different reactivity in an electrolyte
- Two or more cells connected in series
- An electrochemical cell supplied with a continuous fuel and oxygen
14.A simple cell is made from two different metals in contact with an electrolyte. Which of the following statements about how it works are correct? (select all that apply)
Medium
- AThe more reactive metal releases electrons more readily
- BThe more reactive electrode becomes negatively charged
- CElectrons flow through the external circuit to the less reactive electrode
- DThe electrolyte must be a metal
- EBoth electrodes must be made of the same metal
15.A student builds simple cells using copper as one electrode and a series of different metals as the other. Which of the following affect the voltage produced? (select all that apply)
Medium
- AThe difference in reactivity between the two metals
- BThe type of electrolyte used
- CThe size of the voltmeter used
- DThe length of the connecting wires
- EThe colour of the metal electrodes
16.Which of the following are advantages of using hydrogen fuel cells compared with petrol engines in vehicles? (select all that apply)
Medium
- AThey produce no pollution at the point of use, only water
- BThey produce more energy per kilogram than petrol or diesel
- CThey have no moving parts, so less power is lost in transmission
- DThey are quieter, reducing noise pollution
- EThey require high-pressure tanks to store the fuel
17.Which of the following are disadvantages of using hydrogen fuel cells in cars? (select all that apply)
Hard
- AThe materials used to make fuel cells are expensive
- BHigh-pressure tanks are needed to store hydrogen and oxygen
- CFuel cells become less efficient at low temperatures
- DHydrogen is expensive to produce and store
- EThey emit carbon dioxide at the exhaust
18.In a hydrogen fuel cell, the anode is the positive electrode and the cathode is the negative electrode.
Easy
True or false?
19.A battery is made by connecting two or more cells in series to provide a greater voltage.
Easy
True or false?
20.Match each substance in a hydrogen–oxygen fuel cell with its role.
Medium
- Hydrogen
- Oxygen
- Water
- Potassium hydroxide solution
- Fuel that is oxidised at the anode
- Source of oxygen that is reduced at the cathode
- Waste product
- Electrolyte
21.Match each half equation with the electrode in a hydrogen fuel cell where it occurs.
Medium
- 2H₂ → 4H⁺ + 4e⁻
- 4H⁺ + O₂ + 4e⁻ → 2H₂O
- Anode
- Cathode
22.Place the following steps in the correct order to describe how a hydrogen fuel cell produces a potential difference.
Medium
- Hydrogen enters the anode and is oxidised, releasing electrons
- Electrons flow through the external circuit from anode to cathode
- Oxygen enters the cathode and is reduced, gaining electrons
- Water is produced as the only chemical product
23.A student sets up a simple cell with a silver electrode and a tin electrode in an electrolyte. The voltmeter reads 0.8 V. The student replaces the tin electrode with a chromium electrode. Predict the new voltage reading.
Medium
- A0.8 V
- B1.3 V
- C3.4 V
- D2.1 V
24.A simple cell is made using copper and zinc electrodes. The voltage is 1.10 V. Another cell is made using copper and magnesium electrodes. Which statement explains why the voltage is different?
Hard
- AMagnesium is less reactive than zinc, so the voltage is smaller.
- BMagnesium is further from copper in the reactivity series than zinc is, so the voltage is greater.
- CThe electrolyte is different in the two cells.
- DThe copper electrode is the negative electrode in both cells.
25.A student builds a simple cell using two different metals in an electrolyte. Which of the following changes would increase the voltage produced? (select all that apply)
Medium
- AUsing two metals that are further apart in the reactivity series
- BUsing two identical metal electrodes
- CChanging the electrolyte to one whose ions react differently with the electrodes
- DUsing a metal that is less reactive than copper for both electrodes
- EIncreasing the difference in reactivity between the two electrodes
26.In a simple cell, the more reactive metal becomes the negative electrode.
Easy
True or false?
27.A student connects four 1.5 V cells in series to make a battery. What is the total voltage of the battery?
Medium
- A1.5 V
- B3.0 V
- C4.5 V
- D6.0 V
28.Which statement about rechargeable cells is correct?
Medium
- AThe chemical reactions are reversed when an external electrical current is supplied.
- BThe chemical reactions stop permanently when one reactant is used up.
- CThey are non-rechargeable because the reaction is irreversible.
- DThey produce electricity only until the fuel is used up.
29.In a hydrogen fuel cell, hydrogen enters at the anode. What happens to the hydrogen at the anode?
Medium
- AIt is reduced, gaining electrons.
- BIt is oxidised, losing electrons.
- CIt is combusted, producing carbon dioxide.
- DIt is unchanged, acting only as a catalyst.
30.Which of the following is the correct half equation for the reaction at the cathode in a hydrogen fuel cell?
Hard
- A2H₂ → 4H⁺ + 4e⁻
- B4H⁺ + O₂ + 4e⁻ → 2H₂O
- C2H₂ + O₂ → 2H₂O
- DO₂ + 2H₂O + 4e⁻ → 4OH⁻
31.Which statement about the electrodes in a hydrogen fuel cell is correct?
Medium
- AThe anode is negative and the cathode is positive.
- BThe anode is positive and the cathode is negative.
- CBoth electrodes are positive.
- DBoth electrodes are negative.
32.A student wants to make a simple cell. Which set of apparatus is essential?
Medium
- ATwo electrodes made of different metals and an electrolyte
- BTwo electrodes made of the same metal and an electrolyte
- CTwo electrodes made of different metals and a solid insulator
- DOne electrode and a voltmeter only
33.In a simple cell, which electrode becomes the negative electrode?
Medium
- AThe more reactive metal
- BThe less reactive metal
- CThe electrode made of copper
- DThe electrode that gains electrons
34.A simple cell is made using copper and zinc electrodes in an electrolyte. The voltage is 1.10 V. Another cell is made using copper and magnesium electrodes. Which statement explains why the voltage is different?
Medium
- AMagnesium is further from copper in the reactivity series, so the difference in reactivity is greater.
- BMagnesium is closer to copper in the reactivity series, so the difference in reactivity is smaller.
- CThe electrolyte used in the second cell is different.
- DThe copper electrode becomes the negative electrode in the second cell.
35.Which of the following is a non-rechargeable cell?
Medium
- AAlkaline battery
- BLead-acid car battery
- CLithium-ion battery
- DNickel-cadmium battery
36.A student sets up a simple cell with a silver electrode and a tin electrode in an electrolyte. The voltmeter reads 0.8 V. The student replaces the tin electrode with a chromium electrode. Predict the new voltage.
Medium
- AGreater than 0.8 V because chromium is more reactive than tin
- BLess than 0.8 V because chromium is less reactive than tin
- CExactly 0.8 V because the electrolyte has not changed
- D0 V because chromium and silver are both metals
37.A student builds a simple cell using two different metals in an electrolyte. Which change would increase the voltage produced?
Medium
- AUsing metals that are further apart in the reactivity series
- BUsing metals that are closer together in the reactivity series
- CUsing the same metal for both electrodes
- DRemoving the electrolyte
38.In a hydrogen fuel cell, which statement about the electrodes is correct?
Medium
- AThe anode is negative and the cathode is positive.
- BThe anode is positive and the cathode is negative.
- CBoth electrodes are negative.
- DBoth electrodes are positive.
39.Which of the following is the correct half equation for the reaction at the anode in a hydrogen fuel cell?
Medium
- A2H2 → 4H+ + 4e–
- B4H+ + O2 + 4e– → 2H2O
- C2H2 + O2 → 2H2O
- DO2 + 4e– → 2O2–
40.Which of the following is a disadvantage of using hydrogen fuel cells in cars?
Medium
- AHigh pressure tanks are needed to store hydrogen, which are dangerous and difficult to handle.
- BThey produce carbon dioxide when in use.
- CThey need to be recharged from the mains.
- DThey are very noisy.
41.Complete the word equation for the reaction in a hydrogen fuel cell.
Easy
hydrogen + ____ → water
42.A battery is made by connecting four 1.5 V cells in series. What is the total voltage of the battery?
Medium
43.Name the only chemical product formed when a hydrogen–oxygen fuel cell operates.
Easy
44.Complete the sentences about rechargeable and non-rechargeable cells using the words from the box: stops, reverses.
Medium
In non-rechargeable cells, the reaction ____ when one of the reactants has been used up. In rechargeable cells, the reaction ____ when an external electrical current is supplied.
45.Complete the sentences about cells and batteries using the words from the box: series, parallel, reversed, stopped.
Easy
A battery consists of two or more cells connected in ____. In a rechargeable battery, the chemical reactions are ____ when an external electrical current is supplied.
46.Complete the sentences about non-rechargeable and rechargeable cells using the words from the box: stops, reverses, speeds up, slows down.
Medium
In non-rechargeable cells, the reaction ____ when one of the reactants has been used up. In rechargeable cells, the reaction ____ when an external electrical current is supplied.
47.A battery is made by connecting six 1.5 V cells in series. What is the total voltage of the battery?
Medium
48.A cell is made from copper and tin electrodes and produces 0.48 V. A second cell is made from copper and magnesium electrodes and produces 2.71 V. What is the difference in voltage between the two cells?
Medium
49.Complete the sentence about a battery.
Medium
A battery consists of two or more cells connected in ____ to provide a greater voltage.
50.A battery is made by connecting eight 1.5 V cells in series. What is the total voltage of the battery?
Easy
51.Complete the sentences about a simple cell using the words from the box: oxidation, reduction, negative, positive.
Medium
In a simple cell, the more reactive metal releases electrons and becomes the ____ electrode. The less reactive metal gains a more ____ charge.
52.Name the electrolyte commonly used in a hydrogen fuel cell.
Medium
53.Explain why a simple cell made from magnesium and copper produces a greater voltage than one made from zinc and copper.
Medium
54.Explain why hydrogen fuel cells are described as a clean source of energy, but their overall environmental impact may still be a concern.
Hard
55.Explain how the voltage of a simple cell depends on the metals used for the electrodes.
Hard
56.Evaluate the use of hydrogen fuel cells in vehicles compared with petrol engines.
Hard
57.A battery is made by connecting four 1.5 V cells in series. What is the total voltage of the battery?
Medium
- A7 V
- B5 V
- C8 V
- D6 V
58.A battery is made by connecting six 1.5 V cells in series. What is the total voltage of the battery?
Medium
- A10 V
- B9 V
- C8 V
- D11 V
59.A cell is made from copper and tin electrodes and produces 0.48 V. A second cell is made from copper and magnesium electrodes and produces 2.71 V. What is the difference in voltage between the two cells?
Medium
- A3.23 V
- B4.23 V
- C1.23 V
- D2.23 V
60.A battery is made by connecting eight 1.5 V cells in series. What is the total voltage of the battery?
Easy
- A12 V
- B13 V
- C11 V
- D14 V

Thẻ ghi nhớ

What is a simple chemical cell made from?

Two electrodes made from metals of different reactivity, immersed in an electrolyte and connected by wires to an external circuit.

What happens at the more reactive electrode in a simple cell?

The more reactive metal releases electrons more easily, giving that electrode a negative charge.

Why does a simple cell produce a voltage?

The difference in the ability of the two electrodes to release electrons causes a charge difference and therefore a voltage.

How does the reactivity of the two metals affect the voltage of a cell?

The greater the difference in reactivity between the two metals, the greater the voltage produced.

What effect does the electrolyte have on the voltage of a cell?

Different electrolytes contain different ions that react with the electrodes in different ways, so the voltage can change.

What happens to the voltage if both electrodes are made of the same metal?

The voltage is 0 V because there is no difference in reactivity between the electrodes.

How is a battery made from cells?

A battery consists of two or more cells connected in series, which adds their voltages together to give a larger overall voltage.

What voltage is produced by three 1.5 V cells connected in series?

4.5 V, because the voltages of cells in series add up.

Why do non-rechargeable cells eventually stop producing electricity?

The chemical reaction stops when one of the reactants is used up, so no more electricity is produced.

Give an example of a non-rechargeable cell or battery.

Alkaline batteries are non-rechargeable.

How can a rechargeable cell be recharged?

By supplying an external electrical current, which reverses the chemical reactions so the cell can be used again.

What is a fuel cell?

An electrochemical cell in which a fuel donates electrons at one electrode and oxygen gains electrons at the other, producing a voltage.

What is the overall reaction in a hydrogen-oxygen fuel cell?

Hydrogen is oxidised and oxygen is reduced, producing water: 2H₂ + O₂ → 2H₂O.

What is the only chemical product of a hydrogen-oxygen fuel cell?

Water.

In a hydrogen fuel cell, what happens at the anode?

Hydrogen is oxidised, releasing electrons: 2H₂ → 4H⁺ + 4e⁻.

In a hydrogen fuel cell, what happens at the cathode?

Oxygen is reduced, gaining electrons to form water: 4H⁺ + O₂ + 4e⁻ → 2H₂O.

Which electrode is negative in a hydrogen fuel cell?

The anode is the negative electrode and the cathode is the positive electrode.

Give two advantages of using hydrogen fuel cells instead of rechargeable cells and batteries.

They produce no pollution (only water) and they produce more energy per kilogram than petrol or diesel.

Give two disadvantages of using hydrogen fuel cells in vehicles.

Hydrogen is expensive to produce and store, and high-pressure tanks are needed to store the gases, which are dangerous and difficult to handle.

Why do hydrogen fuel cells keep producing electricity as long as fuel is supplied?

They are a continuous process: the fuel is oxidised electrochemically within the cell, so they do not run down like a battery.

What is the difference between a cell and a battery?

A cell is a single electrochemical unit; a battery consists of two or more cells connected in series.

How can the relative reactivity of metals be deduced from cell voltage data?

The greater the voltage between two metals, the greater the difference in their reactivity; the most reactive metal gives the highest voltage with a fixed reference electrode.

Why is a hydrogen fuel cell considered a clean source of energy?

Its only chemical product is water, so it does not produce pollutants such as carbon dioxide or nitrogen oxides.

What are the half equations for the electrode reactions in a hydrogen fuel cell?

Anode: 2H₂ → 4H⁺ + 4e⁻. Cathode: 4H⁺ + O₂ + 4e⁻ → 2H₂O.

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